Critical Temperature Regime Research Articles

Toward Direct Growth of Ultra‐Flat Graphene (Adv. Funct. Mater. 42/2022)

Ultra-Flat Graphene In article number 2200428, Tongbo Wei, Jingyu Sun, Zhongfan Liu, and co-workers implement direct growth of wafer-level, ultra-flat graphene without any wrinkles and metallic impurities on quartz via the inhibition of textured SiOx seed, identification of the critical temperature regime, and in-situ flattening of the substrate surface.

Toward Direct Growth of Ultra‐Flat Graphene

AbstractThe elimination of wrinkles has become a research hotspot in the realm of the chemical vapor deposition growth of graphene, and there have been reliable routes developed for the scenario of catalytic synthesis on metals. Nonetheless, the transfer‐free growth of graphene over insulating substrates affording ultra‐flatness remains a puzzle. Here, the authors report the direct preparation of ultra‐flat graphene on an economical quartz glass substrate at a wafer level, without any wrinkles and metallic impurities, is reported. Density functional theory calculations are employed to establish that graphene adlayer is prone to generate in the presence of textured particulates. In parallel, a critical temperature regime (1443–1453 K), is identified within which graphene adlayer‐restrained forming and substrate in‐situ flattening could simultaneously occur. The thus‐obtained graphene enables the atomically smooth growth of a GaN film with (001) single‐crystallinity over the amorphous substrate. This technique is particularly attractive in the context of cost‐effective integration of emerging III‐nitrides toward exciting applications.

BEHAVIORAL HIDDENTESTING OF DISTRIBUTED INFORMATION SYSTEMSTAKING INTO ACCOUNTOF ENERGY

The introduction of new energy-consuming properties for positions and transitions into the checked properties of the extended reference Petri net, for which the deviations of the tested Petri net are determined and a testing model is developed, provides new diagnostic possibilities. Keeping the class of checked properties in the composition of deviations of incidence relations, correspondences and marking functions of positions and transitions for the checked and reference Petri nets, the new properties make it possible to record the appearance of critical temperature regimes that are a consequence of errors or directly leading to their appearance. Thisversatility of testing helps to increase its completeness, accuracy and efficiency. The energy-heavy testing model is based on verification of incidence, correspondence, and markup functions. Checking the markup functions when generating events in positions, performing actions in transitions, as well as the proposed checking of the energy consumption indicators accumulated in the monitor tokens, is performed when checking the incidence, correspondences. The features of the testingmodel include the input of generalized energy-loaded Petri nets recorders, accumulating information about energy consumption in the behavior of positions/transitions, topological componentsand subnets, the entire Petri net in the process of its functioning. The testingmodel is also distinguished by the recognition of the reference energy-loaded behavior when checking the Petri net based on behavioral identification and coincidenceof subsets of positions/transitions, the determination of behavior, the use of checkprimitives and transactions. The behavioral testingmodel defines the formal conditions for behavioral testingprocedures, including the analysis of the correctness of energy consumption. The dimensionality of the testingmodel was estimated using the representation of Petri net graphs, special graphs of attainable states, including Rabin-Scott automata, using list structures. These estimates define the limits of applicability of the formal testingmodel.

Hot Work Tool Steel Processed by Laser Powder Bed Fusion: A Review on Most Relevant Influencing Factors

As a representative of a common carbon‐bearing hot work tool steel AISI H13 is in focus of the present review paper. Most relevant details for processing of AISI H13 by laser powder bed fusion (L‐PBF) are systematically investigated. Three common stages of process parameter development and material assessment, respectively, are in focus: general processibility, process refinement, and deduction of process–microstructure–property relations, i.e., understanding of the interplay of relevant elementary mechanisms. On the one hand, the routine of AISI H13 processing by L‐PBF is optimized for industrial application. This optimization includes laser parameters, heat treatment, and process sensitivity concerning the used machine and powder. On the other hand, the cluster‐like melt pool microstructure and the formation of various defects during L‐PBF processing of AISI H13 powder are under investigation. Most importantly, understanding of solidification cracking based on critical temperature regimes and residual stress cracking related to martensitic transformation is essential for robust process and material development for the L‐PBF process.

Effects of hydropower development on aquatic eco-environment and adaptive managements

Eco-environmental conservation has been a long challenge and even bottleneck for sustainable hydropower development. This study comprehensively reviewed the advances of researches on river damming impacts on biogeochemical cycling and thereby the aquatic eco-environment effects, zoobenthos habitat, fish habitat and migration routes, as well as structure and non-structure conservation measures. It analyzed the current challenges in fundamental researches and engineering applications as well as the underlying reasons, and highlighted the core aspects for future investigations. These include:① Long-term in-situ monitoring to discover the interception, transformation and transport processes of biogenic elements, and reveal the associated mechanism as well as the accumulated eco-environmental impacts; ② Reservoir induced changes in effective accumulated temperature regime for fish gonadal development and critical temperature regime for fish spawning, and consequently their joint effects on fish reproduction. In particular, the study pointed out the irrationality of some mandatory measures for indigenous fish conservation at present, and proposed the options such as ecological flow and tributary habitat compensation for high dams, and finally it provided some novel technologies to quantitatively assess the efficiency of conservation measures.

Thermal metamorphic history of Antarctic CV3 and CO3 chondrites inferred from the first- and second-order Raman peaks of polyaromatic organic carbon

AbstractParent body thermal metamorphism is an important process that alters the structure of organic matter in the parent asteroid of meteorites. Increasing and progressing thermal metamorphism results in carbonization and graphitization of carbonaceous matter in the parent body. Such modifications in the carbon structures can be studied by Raman microspectroscopy, thanks to its high sensitivity to structure and bonding within carbonaceous molecules. We have characterized polyaromatic carbonaceous matter in a total of 24 Antarctic CV3 and CO3 chondrites using micro-Raman imaging spectroscopy in an effort to better understand parent body thermal metamorphism and assess its effects on the carbon structures. Raman spectral parameters of the first-order carbon peaks (D and G) were extracted from at least 200 spectra for each meteorite and were compared to deduce relationships that yield information regarding the thermal metamorphism conditions. We also show, for the first time, spectral trends and relations of the second-order carbon peaks (2D and D+G) within the 2500–3200 cm−1 with thermal metamorphic history. The second-order peaks appear to contain information that is lacking in the first-order peaks. Based on the second-order carbon peak parameters, we tentatively classify four CV3 chondrites into subtypes, and reclassify another. Peak metamorphic temperatures of the investigated meteorites have been estimated based on the width of the D band as well as the calculated Raman spectral curvature. Estimated temperatures appear to correlate well with the assigned petrologic types. We have calculated higher peak metamorphic temperatures for the CV3 chondrites than for the considered CO3 chondrites and further showed that the peak metamorphic temperatures of CV3oxA chondrites are higher than those of CV3oxB, indicating possibly different metamorphic conditions for the two oxidized subtypes. We observe that there is a relatively larger temperature increase going from CO3.2 to CO3.4 (150 °C increase) compared to CO3.4–CO3.6 (20 °C), which may indicate that the graphitization and structural ordering of carbon reach a critical temperature regime around petrologic type CO3.3.

Anisotropy field and dynamic coercivity of L10 FePt nanoparticles close to the Curie temperature

An investigation of the intrinsic and dynamic coercivity of L10 FePt nanoparticles close to but below the Curie temperature is presented using Langevin dynamics simulations based on an atomistic spin and also a Landau–Lifshitz–Bloch (LLB) macrospin model. The anisotropy field in the critical temperature regime is best defined as the minimum reverse field along the easy axis resulting in switching by spontaneous thermal fluctuations of the magnetization. The temperature dependence of the anisotropy field for the classical spin model is then given by the relation HK(T)≃HK(0)(1−T∕Tc)1−β, where β=0.366 is the critical exponent of the 3D Heisenberg model involved in the temperature dependence of the magnetization. The dynamic coercivity in the thermo-activated regime exhibits a logarithmic time dependence. No transition from elliptical to linear magnetic reversal is observed for 3nm FePt nanoparticles, when the temperature is increased beyond the Curie point, which is a finite size effect.

Observation of hopping transitions for delocalized electrons by temperature-dependent conductance in silicon junctionless nanowire transistors**Project supported by the National Key R&D Program of China (Grant No. 2016YFA0200503) and the National Natural Science Foundation of China (Grant No. 61327813).

We demonstrate transitions of hopping behaviors for delocalized electrons through the discrete dopant-induced quantum dots in n-doped silicon junctionless nanowire transistors by the temperature-dependent conductance characteristics. There are two obvious transition platforms within the critical temperature regimes for the experimental conductance data, which are extracted from the unified transfer characteristics for different temperatures at the gate voltage positions of the initial transconductance gm peak in Vg1 and valley in Vg2. The crossover temperatures of the electron hopping behaviors are analytically determined by the temperature-dependent conductance at the gate voltages Vg1 and Vg2. This finding provides essential evidence for the hopping electron behaviors under the influence of thermal activation and long-range Coulomb interaction.

Hot or not? Comparative behavioral thermoregulation, critical temperature regimes, and thermal tolerances of the invasive lionfish Pterois sp. versus native western North Atlantic reef fishes

Temperature influences the geographic range, physiology, and behavior of many ectothermic species, including the invasive lionfish Pterois sp. Thermal parameters were experimentally determined for wild-caught lionfish at different acclimation temperatures (13, 20, 25 and 32 °C). Preferences and avoidance were evaluated using a videographic shuttlebox system, while critical thermal methodology evaluated tolerance. The lionfish thermal niche was compared experimentally to two co-occurring reef fishes (graysby Cephalopholis cruentata and schoolmaster Lutjanus apodus) also acclimated to 25 °C. The physiologically optimal temperature for lionfish is likely 28.7 ± 1 °C. Lionfish behavioral thermoregulation was generally linked to acclimation history; tolerance and avoidance increased significantly at higher acclimation temperatures, but final preference did not. The tolerance polygon of lionfish shows a strong correlation between thermal limits and acclimation temperature, with the highest CTmax at 39.5 °C and the lowest CTmin at 9.5 °C. The tolerance range of invasive lionfish (24.61 °C) is narrower than those of native graysby (25.25 °C) and schoolmaster (26.87 °C), mostly because of lower thermal maxima in the former. Results show that lionfish display “acquired” thermal tolerance at higher and lower acclimation temperatures, but are no more eurythermal than other tropical fishes. Collectively, these results suggest that while lionfish range expansion in the western Atlantic is likely over the next century from rising winter sea temperatures due to climate change, the magnitude of poleward radiation of this invasive species is limited and will likely be equivalent to native tropical and subtropical fishes with similar thermal minima.

A critical temperature regime for poly(3-hexylthiophene) dissolution in concentrated solutions of ortho-dichlorobenzene

We report the thermo-assisted dissolution of aggregated regioregular poly(3-hexylthiophene) (P3HT) in ortho-dichlorobenzene (o-DCB) at a concentration level that is typical for photovoltaic applications (20mg/mL). Detailed investigation on electronic absorption and fluorescence spectroscopy revealed, for the dissolution of P3HT aggregates, a critical temperature regime (27–33°C) with a middle-point temperature (Tm∼29°C) and an aggregation-degree dependent endothermic dissolution enthalpy. In this temperature regime, pre-resonant Raman spectroscopy results showed a drastic variation of solvent–solute interaction in the solvation sphere of P3HT. In addition, an annealing treatment to the concentrated solution is proven to be rather effective in minimizing P3HT agglomeration.

Role of the core energy in the vortex Nernst effect

We present an analytical study of diamagnetism and transport in a film with superconducting phase fluctuations, formulated in terms of vortex dynamics within the Debye-H\"uckle approximation. We find that the diamagnetic and Nernst signals decay strongly with temperature in a manner which is dictated by the vortex core energy. Using the theory to interpret Nernst measurements of underdoped La$_{2-x}$Sr$_x$CuO$_4$ above the critical temperature regime we obtain a considerably better fit to the data than a fit based on Gaussian order-parameter fluctuations. Our results indicate that the core energy in this system scales roughly with the critical temperature and is significantly smaller than expected from BCS theory. Furthermore, it is necessary to assume that the vortex mobility is much larger than the Bardeen-Stephen value in order to reconcile conductivity measurements with the same vortex picture. Therefore, either the Nernst signal is not due to superconducting phase fluctuations, or that vortices in underdoped La$_{2-x}$Sr$_x$CuO$_4$ have highly unconventional properties.

Temperature effects on intrachain recombination of bipolarons in conjugated polymers

The temperature influence over the intrachain recombination dynamics between oppositely charged bipolarons has been theoretically investigated using a version of the Su–Schrieffer–Heeger model. The results shown that, below of a critical temperature regime, these charge carriers can recombine into a biexciton. This excited state is a light emissive specie that can emit one photon and turn into an exciton state. This specie can thereafter decay to the ground state by other photon emission. This knowledge can enlighten the understanding needed to improve the internal quantum efficiency of electroluminescence in Polymer Light Emitting Diodes.

Temperature effects on the scattering of polarons and bipolarons in organic conductors.

The scattering process between an electron-polaron and a hole-bipolaron has been simulated using a version of the Su-Schrieffer-Heeger (SSH) model modified to include an external electric field, Coulomb interactions, and temperature effects in the scope of nonadiabatic molecular dynamics. The simulations reveal remarkable details concerning the polaron-bipolaron recombination reaction. It is found that there exists a critical temperature regime below which a hole-bipolaron and a mixed state composed by an electron-polaron and an exciton are formed and a hole-bipolaron and a free electron are the resulting products of the collisional process, if the temperature is higher than the critical value. In addition, it is obtained that both channels depend sensitively on the strength of the applied electric field. These significant results may provide guidance to understand processes regarding electroluminescence in polymer diodes.

Identifying gaps in flaring Herbig Ae/Be disks using spatially resolved mid-infrared imaging

*Context The evolution of young massive protoplanetary disks toward planetary systems is expected to include the formation of gaps and the depletion of dust and gas. *Aims A special group of flaring disks around Herbig Ae/Be stars do not show prominent silicate emission features. We focus our attention on four key Herbig Ae/Be stars to understand the structural properties responsible for the absence of silicate feature emission. *Methods We investigate Q- and N-band images taken with Subaru/COMICS, Gemini South/T-ReCS and VLT/VISIR. Our radiative transfer modeling solutions require a separation of inner- and outer- disks by a large gap. From this we characterize the radial density structure of dust and PAHs in the disk. *Results The inner edge of the outer disk has a high surface brightness and a typical temperature between ~100-150 K and therefore dominates the emission in the Q-band. We derive radii of the inner edge of the outer disk of 34, 23, 30 and 63 AU for HD97048, HD169142, HD135344B and Oph IRS 48 respectively. For HD97048 this is the first detection of a disk gap. The continuum emission in the N-band is not due to emission in the wings of PAHs. This continuum emission can be due to VSGs or to thermal emission from the inner disk. We find that PAH emission is not always dominated by PAHs on the surface of the outer disk. *Conclusions. The absence of silicate emission features is due to the presence of large gaps in the critical temperature regime. Many, if not all Herbig disks with Spectral Energy Distribution (SED) classification `group I' are disks with large gaps and can be characterized as (pre-) transitional. An evolutionary path from the observed group I to the observed group II sources seems no longer likely. Instead, both might derive from a common ancestor.

Crystallization Kinetics in High-rate Electron Beam Evaporated Poly-Si Thin Film Solar Cells on ZnO:Al

AbstractThe microstructure and crystallization kinetics of electron beam evaporated Si on ZnO:Al coated glass for polycrystalline solar cells was studied by electron backscatter diffraction and optical microscopy at various deposition temperatures. A time dependent analysis of the dynamics of the crystallization allowed for the individual determination of growth and nucleation processes. The nucleation process of Si on ZnO:Al was found to be influenced by a variation of the deposition temperature of the amorphous Si in a critical temperature regime of 200 ˚C to 300 ˚C. The nucleation rate decreased significantly with decreasing deposition temperature, while the activation energy for nucleation increased from 2.9 eV at a deposition temperature of 300 ˚C to 5.1 eV at 200 ˚C, resulting in poly-Si which comprised grains with features sizes of several μm.

Estimation in spin glasses: A first step

The Sherrington–Kirkpatrick model of spin glasses, the Hopfield model of neural networks and the Ising spin glass are all models of binary data belonging to the one-parameter exponential family with quadratic sufficient statistic. Under bare minimal conditions, we establish the $\sqrt{N}$-consistency of the maximum pseudolikelihood estimate of the natural parameter in this family, even at critical temperatures. Since very little is known about the low and critical temperature regimes of these extremely difficult models, the proof requires several new ideas. The author’s version of Stein’s method is a particularly useful tool. We aim to introduce these techniques into the realm of mathematical statistics through an example and present some open questions.

Selective effect of the duration of the critical temperature period on some allozyme loci of Atlantic salmon Salmo salar L. (Salmonidae)

Genetic structure of juvenile fish from the populations of the Atlantic salmon Salmo salar inhabiting the rivers of Murmansk oblast, Arkhangelsk oblast, and Karelia, as well as of juveniles from hatcheries was examined at five allozymic loci: aspartate aminotransferase (AAT-4*), isocitrate dehydrogenase (IDHP-3*), iditol dehydrogenase (IDDH-2*), esterase D (ESTD*), and malic enzyme (MEP-2*). High genetic differentiation of both natural and "hatchery" juvenile fish was revealed. It was demonstrated that the gene pool of juveniles at three of the five loci tested was to a considerable degree formed by natural selection. In this case, the role of limiting factor was played by the duration of critical temperature regime in the rivers. The differentiation factors for juveniles from nature were not established, however, their clusterization pattern pointed to a possible role of natural selection in this process.

Brine percolation and the transport properties of sea ice

AbstractSea ice is distinguished from many other porous composites, such as sandstones or bone, in that its microstructure and bulk material properties can vary dramatically over a small temperature range. For brine-volume fractions below a critical value of about 5%, which corresponds to a critical temperature of about −5°C for salinity of 5 ppt, columnar sea ice is effectively impermeable to fluid transport. For higher brine volumes, the brine phase becomes connected and the sea ice is permeable, allowing transport of brine, sea water, nutrients, biomass and heat through the ice. Over the past several years it has been found that brine transport is fundamental to such processes as sea-ice production through freezing of flooded ice surfaces, the enhancement of thermal and salt fluxes through sea ice, nutrient replenishment for sea-ice algal communities, and to sea-ice remote sensing. Motivated by these observations, recently we have shown how percolation theory can be used to understand the critical behavior of fluid transport in sea ice. We applied a percolation model developed for compressed powders of large polymer particles with much smaller metal particles, which explains the observed behavior of the fluid permeability in the critical temperature regime, as well as Antarctic data on surface flooding and algal growth rates. Moreover, the connectedness properties of the brine phase play a significant role in the microwave signature of sea ice through its effective complex permittivity and surface flooding. Here we review our recent results on brine percolation and its role in understanding the fluid and electromagnetic transport properties of sea ice. We also briefly report on measurements of percolation we made on first-year sea ice during the winter 1999 Mertz Glacier Polynya Experiment.

Direct experimental determination of the gap exponent Δ in two three-dimensional Heisenberg ferromagnets

Measurements of the longitudinal adiabatic and isothermal susceptibility in the critical temperature regime of magnetic ordering lead to a direct determination of the so-called gap exponent Δ. This is illustrated for two three-dimensional Heisenberg ferromagnets Rb 2CuBr 4ṡ2H 2O and (NH 4) 2CuBr 4ṡ2H 2O. Within experimental error there is complete agreement between Δ obtained directly from this method and that derived from critical exponents α and β (with the aid of scaling relations). This implies that, in general, α and β can be determined by measuring (with only one experimental technique) Δ and γ.

Stability of the Defect State in Neutron-Irradiated Molybdenum

The thermal stability of neutron-induced defects in molybdenum irradiated in Experimental Breeder Reactor II (EBR-II) to a fast-neutron fluence of ∼1 × 1022 n/cm2 (E >1 MeV) clearly suggests that there are critical temperature regimes that should be avoided by reactor design engineers. These regions are manifested by a rapid change in the micro structure within a small temperature interval, a circumstance that can significantly influence the strength and corresponding ductility of the material. One critical temperature occurs at ∼800°C, where the irradiation-induced modulus-corrected strength could vary significantly compared to unirradiated molybdenum for a small temperature variation around 800°C.Voids have been shown to occur in specimens irradiated at 430, 580, 700, 800, 900, and 1000°C; these voids are stable at temperatures up to ∼0.60 Tm, rather than the 0.55 Tm value reported earlier for low fluence irradiations. The increase in the complete void removal temperature is suggested to exist due to the presence of a larger void size and the ordered void lattice structure in EBR-II samples.