Sink Density Research Articles

Complex dislocation loop networks as natural extensions of the sink efficiency of saturated grain boundaries in irradiated metals.

The development of radiation-tolerant structural materials is an essential element for the success of advanced nuclear energy concepts. A proven strategy to increase radiation resistance is to create microstructures with a high density of internal defect sinks, such as grain boundaries (GBs). However, as GBs absorb defects, they undergo internal transformations that limit their ability to capture defects indefinitely. Here, we show that, as the sink efficiency of GBs becomes exhausted with increasing irradiation dose, networks of irradiation loops form in the vicinity of saturated or near-saturated GB, maintaining and even increasing their capacity to continue absorbing defects. The formation of these networks fundamentally changes the driving force for defect absorption at GB, from "chemical" to "elastic." Using thermally-activated dislocation dynamics simulations, we show that these networks are consistent with experimental measurements of defect densities near GB. Our results point to these networks as a natural continuation of the GB once they exhaust their internal defect absorption capacity.

Effect of Production Bias on Radiation-Induced Segregation in Ni-Cr Alloys

We present an in-depth investigation into the Radiation-Induced Segregation (RIS) phenomenon in Ni-Cr alloys. All the pivotal factors affecting RIS such as surface’s absorption efficiency, grain size, production bias, dose rate, temperature, and sink density were systematically studied. Through comprehensive simulations, the individual and collective impacts of these factors were analyzed, enabling a refined understanding of RIS. A notable finding was the significant influence of production bias on point defects’ interactions with grain boundaries/surfaces, thereby playing a crucial role in RIS processes. Production bias alters the neutrality of these interactions, leading to a preferential absorption of one type of point defect by the boundary and consequent establishment of distinct surface-mediated patterns of point defects. These spatial patterns further result in non-monotonic spatial profiles of solute atoms near surfaces/grain boundaries, corroborated by experimental observations. In particular, a positive production bias, signifying a higher production rate of vacancies over interstitials, drives more Cr depletion at the grain boundary. Moreover, a temperature-dependent production bias must be considered to recover the experimentally reported dependence of RIS on temperature. The severity of radiation damage and RIS becomes more pronounced with increased production bias, dose rate, and grain size, while high temperatures or sink density suppress the RIS severity. Model predictions were validated against experimental data, showcasing robust qualitative and quantitative agreements. The findings pave the way for further exploration of these spatial dependencies in subsequent studies, aiming to augment the comprehension and predictability of RIS processes in alloys.

Experimental investigation of moisture content on suppressing ignition of accumulated dust

The moisture content sprayed into the dust layer in industrial sites was one of the main factors affecting the occurrence of reignition, which could prevent fire and explosion accidents. Although moisture was traditionally considered to inhibit ignition by endothermic and delayed drying, its effect on the thermophysical properties of the dust layer cannot be ignored due to a certain degree of influence on the heat transfer and heat absorption processes of the dust layer. In present study, six wheat straw samples with MCs from <0.2% to 50% MCs were tested with the hot plate methods, and the heat and mass transfer at four stages during the smouldering processes were discussed. The effect of MC on the ignition time, critical ignition temperature, and mass-loss characteristic parameters of the samples was determined. As MCs increased, the thermal conductivity of the sample increased from 0.110 to 0.248 W/(m·K), as well as the heat sink density (ΔHs) increased from 6.66 × 105 to 16.28 × 105 J/kg. It was necessary to make ΔHs higher than the heat increase value (ΔQ) for suppressing ignition.

The effect of thermal history on the additively manufactured AlSi10Mg alloy response to ion irradiation

Aluminum alloys, mainly from the 5xxx and 6xxx families, are used extensively in research reactors due to their suitable properties. However, alloys common in nuclear applications are not yet suitable for Additive Manufacturing (AM). The alloy AlSi10Mg has good engineering properties and is the most used and investigated AM Al-alloy. In this work, stress relieved (SR) samples of AM AlSi10Mg have been compared to samples that underwent a subsequent heat treatment at 500°C (SHT), producing two distinctly different microstructures. The SHT samples contain larger grains with a cleaner matrix and coarser silicon particles compared to the SR samples. Samples with the two microstructures were irradiated using silicon ions up to damage of ∼20 dpa at a depth of about 1 µm. To compare the response of both conditions to irradiation, properties were measured using nano-indentation and transient grating spectroscopy (TGS). Microstructure was characterized using TEM. Results show that the SHT condition is much more sensitive to irradiation, compared to SR. Irradiation caused thermal diffusivity to decrease by ∼5% in the SR condition and by more than 50% in the SHT condition. Hardness increased by 12 and 24% in the SR and SHT conditions, respectively. Also, the void number density was significantly larger in the SHT condition. No change was observed in young's modulus. The lower sensitivity of the SR condition is attributed to a higher sink density present in the initial microstructure, resulting in overall less irradiation damage retained in the material after irradiation. The explanation offered for the major drop in thermal diffusivity observed only in the SHT condition is the large size of the silicon particles, which increases their instability during irradiation, causing them to partly dissolve and release atomic silicon into the matrix around them. These silicon atoms are effective electron and phonon scatter centers. The findings of this work show that the pre-irradiated microstructure of AM AlSi10Mg has a crucial role in the material's performance in nuclear reactor core conditions. Careful thought and care need to be implemented to the heat treatment applied to an as-built part.

A practical simulation of carbon sink calculation for urban buildings: A case study of Zhengzhou in China

Cement and other cementitious materials in buildings can react with CO2 in atmosphere, leading to the carbonization. Predicting the precise uptake of CO2 of urban buildings is crucial to addressing the loss of carbon sinks. Here, we systematically studied the carbon sinks of urban buildings in the third ring road area of Zhengzhou city. First, we developed an effective model described by the exposed area and completion time of buildings based on Fick's second law. Using this model, we studied the carbon sinks of urban buildings in the past 50 years and predicted the carbon sinks in the next 10 years. The total carbon sink is 1.648 million tons in the last 50 years. The carbon sink density across the study area shows a heterogeneous distribution, with high density concentrated in the central and left half. In addition, carbon sinks exhibit time-dependent characteristics, with the period 2002–2022 accounting for 77.7 % of the total for the entire 60-year period. The carbon sinks and spatial distribution of carbon sink density are not only critical to address lost carbon sinks, but also provides important information for future urban planning and should therefore be of wide interest to environmental scientists, architects and government staff.

Pretreatment of Bituminous Coal By-Products for the Hydrometallurgical Extraction of Rare Earth Elements

Low-temperature plasma (LTP) oxidation has been widely used to study the mineralogy of the mineral matter existing in coal sources. The current study investigated the potential of LTP oxidation as a pre-treatment method to improve rare earth element (REE) leachability from coal and its by-products. Representative density-fractionated samples of Baker and Fire Clay coarse refuse seam materials were ground to a top size of 180 µm and subjected to low-temperature plasma oxidation. Subsequently, the treated samples were leached at 1% w/v solids concentration and 75 °C for 5 h using (i) de-ionized (DI) water, (ii) 0.1 mol/L of ammonium sulfate, and (iii) 1.2 mol/L of sulfuric acid. It was determined that LTP treatment improved REE leaching characteristics, especially the leaching of heavy REEs (HREE), existing in the lighter density fractions of the Baker seam coarse refuse material. For instance, the HREE recovery for the 1.6 specific gravity (SG) float fraction increased from 8% to 33% using 0.1 mol/L of ammonium sulfate solution after 32 h of LTP treatment. This finding indicated that HREEs associated with the organic matter were released by the LTP treatment and adsorbed onto the surfaces of highly negative charged mineral matter and was exchanged with ammonium to allow their recovery. Similarly, when using 1.2 mol/L of sulfuric acid, the HREE recovery increased from 23% to 53% for the 1.6 SG float fraction. Interestingly, LTP oxidation did not provide significant improvement in REE recovery from the 2.2 sink density fractions, which was likely due to its lower organic content. No significant benefits were observed when treating the Fire Clay coarse refuse material, which was likely due to the lack of organic affinity and the difficult-to-leach REE minerals associated with the coal source such as monazite, xenotime, and zircon. Conversely, high-temperature oxidation within a temperature range of 600–750 °C significantly improved REE leaching characteristics for both coal sources. Improvement in REE recovery was due to decarbonization of the material, clay dehydroxylation and subsequent conversion of liberated REE-bearing minerals into a more leachable form. However, increasing the temperature above 800 °C decreased REE recovery due to the conversion of meta-kaolinite into mullite, which is chemically stable.

Carbon Accounting of Weihe CSA Pilot Demonstration Area in Longjiang Forest Industry

Carbon sink afforestation (CSA) has become one of the most concerned issues of countries around the world under the background of climate change. The northern forest ecosystem, located in mid- and high latitudes, is a huge terrestrial carbon pool and is very sensitive to climate change. Studying the carbon emission accounting of CSA in northern forests helps clarify the contribution of CSA to forestry carbon sequestration and forecasts the carbon sink effect of forest ecosystems. It is of great significance for the assessment of forest carbon sink and carbon cycling by providing a scientific basis and reference for the development, utilization, and management of carbon sink afforestation, as well as the coordinated development of ecology and social economy. At present, research on the carbon emission accounting of the CSA in northern China is still lacking. According to the relevant models and parameters of estimating live biomasses with the default method from the IPCC’s (Intergovernmental Panel on Climate Change) Technical Guidelines for National Forestry Carbon Sink Accounting and Monitoring, carbon stock, carbon emission, and carbon leakage of the Weihe CSA (carbon sink afforestation) pilot demonstration area in the boreal Longjiang Forest Industry in a baseline scenario and CSA scenario were measured, and the CSA’s net carbon sink was estimated. The conclusions were as follows: (1) By the end of the crediting period of the project’s baseline, carbon fixation reached 101.85 t CO2, with an average annual CO2 fixation of 5.09 t. By the end of the CSA term, carbon sequestration was accumulated as 382.13 t CO2, with an average annual sequestration of 19.11 t CO2, nearly four times that of the baseline period. (2) By the end of the CSA term, the carbon sequestration of the coniferous standing forest was 46.2% higher than that of the broad-leaved standing forest, accounting for 65% of the total carbon sequestration of the forest. The carbon sequestration of the tree species in the coniferous forest in descending order is Picea koraiensis, Pinus koraiensis, Larix olgensis, Fraxinus mandshurica, and Populus cathayana. The carbon sink density of the coniferous standing forest was 8.7% higher than that of the broad-leaved standing forest. (3) The carbon fixation of the coniferous standing forest nearly doubled that of the broad-leaved standing forest. The highest carbon fixation belongs to Fraxinus mandshurica, closely followed by Picea koraiensis and Pinus koraiensis at a high level, and then Larix olgensis and Populus cathayana. The carbon fixation of Fraxinus mandshurica was 20 times that of Populus cathayana. (4) The accumulated greenhouse gas emissions within the boundary during the CSA period were 2.53 t CO2-e. The accumulated greenhouse gas leakage outside the boundary was 0.05 t CO2-e. Carbon emissions occurred in the first, second, and third years of the crediting period, while carbon leakage occurred only in the first year. (5) This result appeared as carbon sources during the first three years of the CSA period but changed to carbon sink from the fourth year and then accumulated to 280.28 t (70.07 t CO2-e·hm−2) as a net carbon sink by the end of the term. The Weihe CSA appeared to have a relatively strong ability of carbon sequestration in temperate forests. The CSA activity is influenced by factors such as policies, environment, management, etc., resulting in uncertainties in carbon sequestration accounting. Therefore, it is suggested that comparison studies and investigations should be strengthened, and multiple methods should be integrated into carbon sequestration estimation and accounting, leading the carbon accounting of forest ecosystems to a high-level and comprehensive development.

Grain boundary softening from stress assisted helium cavity coalescence in ultrafine-grained tungsten

The formation of helium cavities in coarse-grained materials produces hardening proportional to the number density and size of the cavities and due to the interaction of dislocations with intragranular helium defects. In nanostructured metals containing a high density of interfacial sinks, preferential cavity formation in the grain boundaries instead produces softening that is often attributed to enhanced interfacial plasticity. Employing two grades of ultrafine-grained tungsten, we explore this effect using targeted implantation studies to map cavity evolution as a function of the irradiation conditions and quantify its impact on the mechanical response through nanoindentation. Softening is reported at implantation temperatures above the threshold for preferential grain boundary cavity formation but at a sufficiently low fluence prior to the growth of intragranular cavities. Collective changes in the mean cavity size, density, and morphology beneath a residual impression on an implanted surface indicate that cavity coalescence accompanied the reduction in hardness. Complementary atomistic simulations demonstrate that, in tungsten grain structures exhibiting softening, grain boundary bubble coalescence is driven by stress concentrations that further act to localize strain in the grain boundaries through cooperative deformation processes involving local atomic shuffling and sliding, dislocation emission, and even the nucleation of unstable twinning events.

Computational study of the multidimensional spread of smouldering combustion at different peat conditions

Smouldering combustion is the slow, low-temperature, flameless burning of porous fuels, which propagate both laterally and in-depth. In this study, we build a physics-based two-dimensional model to simulate lateral and in-depth smouldering spread simultaneously based on open-source code Gpyro. We first validate the model against a shallow-reactor experiment (of 1.6 cm thickness) in the literature. Based on the validated model, we then investigate 2D smouldering in a 3 times deeper peat layer at different soil conditions. We found that lateral and in-depth spread rates depend on the organic density and the Oxygen supply. Because of the larger Oxygen supply close to the free surface, the lateral spread is 10 times faster than in-depth spread. In addition, for lateral spread the influence of inorganic density and moisture can be explained by a unified parameter, heat sink density, agreeing with previous experimental results. The model predicts the effects of peat conditions on multidimensional smouldering spread and reveals the controlling mechanisms both lateral and in-depth spread, providing a better understanding of this complex phenomenon.

Connection intervals in multi-scale infrastructure-augmented dynamic networks

We consider a hybrid spatial communication system in which mobile nodes can connect to static sinks in a bounded number of intermediate relaying hops. We describe the distribution of the connection intervals of a typical mobile node, i.e., the intervals of uninterrupted connection to the family of sinks. This is achieved in the limit of many hops, sparse sinks and growing time horizons. We identify three regimes reflecting various degrees of sink densities. Namely, (1) a regime of dense sinks, in which the limit is deterministic and given as an expectation with respect to percolation clusters, (2) a regime of sparse sinks, in which the limit depends on a random number of reachable sinks, and (3) an intermediate critical regime.

Novel effects of grain size and ion implantation on grain boundary segregation in ion irradiated austenitic steel

Nuclear reactor environments are extreme in nature due to the combination of exposure to corrosive coolant, mechanical stresses, and neutron irradiation damage. This combination of environments can lead to irradiation induced/assisted precipitation, segregation, and embrittlement coupled with enhanced creep and stress corrosion cracking. While nanostructured materials are of interest in a variety of applications due to their unique properties including high mechanical strength, for nuclear applications nanostructured materials have the added benefit of irradiation resistance due to the high volume density of sinks for irradiation-induced defects. In this study, we show unique radiation-induced segregation (RIS) behavior in nanocrystalline 304 stainless steel (SS304). Typical RIS in austenitic steels includes Ni enrichment and Cr depletion within the grain boundaries. In nanostructured SS304 this RIS is reduced. Furthermore, interestingly, some grain boundaries in the nanocrystalline SS304 in this study were found to be enriched in Cr after Fe2+ ion irradiation at 500 °C up to 50 displacements per atom (dpa). To understand this unique observation, lattice-based atomic kinetic Monte Carlo simulations were performed to investigate the effects of grain size, thermal segregation, as well as injected interstitials (introduced as Fe self-ions). The results indicate that the Cr enrichment at grain boundaries may be caused by combined effects of grain size, self-ion injection and preferential Cr diffusion via the interstitial mechanism. The findings also suggest a possible difference in RIS between ion and neutron irradiations.

Measurement of Forest Carbon Sink Efficiency and Its Influencing Factors Empirical Evidence from China

The efficiency and productivity improvement are the core requirements of high-quality development, while improving the efficiency of forest carbon sinks is an important means and fundamental way to achieve their high-quality development. Based on the forests and socioeconomic development data of 31 provinces (cities and districts) in China from 2004 to 2018, the biomass method and DEA-Tobit panel regression model were used to analyze the level of forest carbon stock, carbon sink and carbon sink efficiency, and factors influencing forest carbon sink efficiency in China’s provinces. The results indicated that: ① nationwide forest carbon stocks and carbon sinks increased successively while carbon density decreased. The regions with higher carbon stock, carbon sink, and carbon density were concentrated in the northeast and southwest forest areas with abundant forest resources. ② During the 7th to 9th forest inventory, the efficiency of forest carbon sinks was on a low and decreasing trend. The mean values of comprehensive efficiency in general for the 7th to 9th forest inventory periods were 0.421 and 0.336, respectively. The scale efficiency in the decomposition efficiency was above 0.650 for both inventory periods, and gradually increased, showing that the gap between the actual scale and the optimal production scale of forestry carbon sink was decreasing. The pure technical efficiency level represented the production efficiency of input factors at the optimal scale of forestry carbon sinks. The mean values of the two periods are 0.639 and 0.514, respectively, while the differences within the production frontier surface are 0.361 and 0.486, which indicates that there is input redundancy or output deficiency in the two periods as a whole. ③ The total annual precipitation and the level of socioeconomic development have significant driving effects on the improvement of forest carbon sink efficiency, while the incidence of pests and diseases, abnormal changes in temperature, afforestation area and the development of population urbanization have significant inhibiting effects on the improvement of forest carbon sink efficiency in China.

Role of tantalum concentration on the high dose self-ion irradiation behavior of nanocrystalline binary alloys

In this work, the self-ion irradiation behavior of nanocrystalline copper-tantalum alloys was investigated. In particular, the microstructural evolution of Cu-3at.%Ta and Cu-10at.%Ta was evaluated under the fluence of 2 × 1017 ions/cm2 of 4 MeV Cu-ions at different temperatures. Results revealed that despite the ability of Cu-10Ta to reprecipitate new nanoclusters and thereby increase the sink density by ∼17%, it undergoes significant microstructural evolution. On the other hand, Cu-3Ta exhibits a relatively more stable microstructural response and 3.5 times less swelling over the same conditions. This result illustrates the premise that irradiation and deformation may be coupled to stabilize/rejuvenate Ta-nanoclusters in extreme-environments.

Implications of Microstructure in Helium-Implanted Nanocrystalline Metals.

Helium bubbles are known to form in nuclear reactor structural components when displacement damage occurs in conjunction with helium exposure and/or transmutation. If left unchecked, bubble production can cause swelling, blistering, and embrittlement, all of which substantially degrade materials and—moreover—diminish mechanical properties. On the mission to produce more robust materials, nanocrystalline (NC) metals show great potential and are postulated to exhibit superior radiation resistance due to their high defect and particle sink densities; however, much is still unknown about the mechanisms of defect evolution in these systems under extreme conditions. Here, the performances of NC nickel (Ni) and iron (Fe) are investigated under helium bombardment via transmission electron microscopy (TEM). Bubble density statistics are measured as a function of grain size in specimens implanted under similar conditions. While the overall trends revealed an increase in bubble density up to saturation in both samples, bubble density in Fe was over 300% greater than in Ni. To interrogate the kinetics of helium diffusion and trapping, a rate theory model is developed that substantiates that helium is more readily captured within grains in helium-vacancy complexes in NC Fe, whereas helium is more prone to traversing the grain matrices and migrating to GBs in NC Ni. Our results suggest that (1) grain boundaries can affect bubble swelling in grain matrices significantly and can have a dominant effect over crystal structure, and (2) an NC-Ni-based material can yield superior resistance to irradiation-induced bubble growth compared to an NC-Fe-based material and exhibits high potential for use in extreme environments where swelling due to He bubble formation is of significant concern.

Temperature effects on the radiation damage morphology in nanocrystalline iron

While transformations of dislocation-loop character at high temperatures during heavy ion irradiation has been studied for more than two decades, the role of grain size, or high sink density, has not been considered. To interrogate the effect of defect mobility on irradiated nanocrystalline (nc) microstructures at elevated temperatures, detailed in-situ ion irradiation transmission electron microscopy (TEM) studies were carried out. The transformation temperature for the Burgers vector b = 1/2 <111>-to-<100> transition was found to be 450 °C, representing a lower threshold than that found in micron-grain-sized counterparts. The formation of stable b = 1/2<111> dislocation loops is observed below 400 °C, while at 450∼500 °C, 1/2<111> loops either transformed into 〈100〉 loops or were absorbed at grain boundaries (GBs). Thus, the substantial absorption of point defects and dislocation loops by GBs over a range of temperatures characteristically changes the defect morphology from large finger-shaped observed in micron-sized grains to small circular shape loops in nc grains.

Accounting for forest management in the estimation of forest carbon balance using the dynamic vegetation model LPJ-GUESS (v4.0, r9710): implementation and evaluation of simulations for Europe

Abstract. Global forests are the main component of the land carbon sink, which acts as a partial buffer to CO2 emissions into the atmosphere. Dynamic vegetation models offer an approach to projecting the development of forest carbon sink capacity in a future climate. Forest management capabilities are important to include in dynamic vegetation models to account for the effects of age and species structure and wood harvest on carbon stocks and carbon storage potential. This article describes the implementation of a forest management module containing even-age and clear-cut and uneven-age and continuous-cover management alternatives in the dynamic vegetation model LPJ-GUESS. Different age and species structure initialisation strategies and harvest alternatives are introduced. The model is applied at stand and European scales. Different management alternatives are applied in simulations of European beech (Fagus sylvaticus) and Norway spruce (Picea abies) even-aged monoculture stands in central Europe and evaluated against above-ground standing stem volume and harvested volume data from long-term experimental plots. At the European scale, an automated thinning and clear-cut strategy is applied. Modelled carbon stocks and fluxes are evaluated against reported data at the continent and country levels. Including wood harvest in regrowth forests increases the simulated total European carbon sink by 32 % in 1991–2015 and improves the fit to the reported European carbon sink, growing stock, and net annual increment (NAI). Growing stock (156 m3 ha−1) and NAI (5.4 m3 ha1 yr1) densities in 2010 are close to reported values, while the carbon sink density in 2000–2007 (0.085 kg C m−2 yr1) equates to 63 % of reported values, most likely reflecting uncertainties in carbon fluxes from soil given the unaccounted for forest land-use history in the simulations. The fit of modelled and reported values for individual European countries varies, but NAI is generally closer to reported values when including wood harvest in simulations.

Gasification of chars from tetralin liquefaction of &lt; 1.5 g cm−3 carbon-rich residues derived from waste coal fines in South Africa

The float–sink density separation method was used to produce a < 1.5 g cm−3 coal density fraction. The sample was subjected to tetralin liquefaction experiments and pyrolysed to produce char samples. The < 1.5 g cm−3 coal density fraction and its liquefaction carbon-rich residue chars formed from the pyrolysis experiments were evaluated using the CO2 gasification tests. The chars were characterized using a thermogravimetric analyzer by heating the samples at isothermal temperatures between 880 and 940 °C under a CO2 atmosphere. The results obtained from the gasification experiments revealed that the gasification reactivity values (Ri, Rs, Rtf, Rt/0.5) of the liquefaction carbon-rich residue chars were higher than those of the < 1.5 g cm−3 coal density fraction chars. Some inherent mineral matter in the residues may play a catalytic role during gasification of South African lighter density waste coal density fractions and their liquefaction residue chars. The initial reactivity of the liquefaction residue chars was observed to be approximately double than those of the < 1.5 g cm−3 coal density fraction chars. Significant increases in a number of pores were associated with the liquefaction experiments of these carbon-rich particles, which aid in the acceleration of the gasification reactions. These increases in the number of pores assisted the reduction of the gasification activation energy values. The RPM was shown to fit the experimental data the best and used to determine kinetic parameters. The gasification activation energy of the < 1.5 g cm−3 coal density fraction chars was shown to be 190.5 kJ mol−1 and 236.7 kJ mol−1 for Highveld float (HF) and Waterberg float (WF) chars, respectively. The values of the apparent activation energy for the liquefaction carbon-rich residues from the same two < 1.5 g cm−3 coal density fraction residue samples were 145.3 kJ mol−1 for the Highveld coal sample and 196.0 kJ mol−1 for the Waterberg coal sample. The gasification results obtained in this study indicate that the possibility of utilizing the waste coal floats and their liquefaction carbon-rich residues in the thermochemical processes (pyrolysis and gasification) is high.

Microstructures and mechanical properties of a modified 9Cr ferritic-martensitic steel in the as-built condition after additive manufacturing

A newly developed nano-structured high-Mn 9Cr ferritic-martensitic (FM) steel designed for additive manufacturing (Additive-manufactured Nanostructured Alloy, ANA) was fabricated via the direct energy deposition method. The as-printed ANA2 showed tensile properties (strength and elongation) and Charpy impact toughness (upper-shelf energy and ductile-brittle transition temperature) comparable to oxide-dispersion-strengthened (ODS) Eurofer and PM2000. Compared with wrought P91, the as-built ANA2 showed significantly higher yield strength but inferior Charpy impact toughness and ductility. Microstructural characterization revealed uniformly distributed sub-micron pores, an extremely high dislocation density, and a high density of ultrafine nano-structured precipitates in the matrix. The microstructures indicated the dislocations as the dominant strengthening element and the ultrafine precipitates as the primary contribution to estimated irradiation sink density. This work demonstrates the ability to exploit the unique consolidation properties of additive manufacturing to fabricate steels which marry the benefits of both ODS alloys and conventionally processed FM steels.

A novel framework for energy‐efficient compressive data gathering in heterogeneous wireless sensor network

SummaryWireless sensor network (WSN) suffers from the energy‐limited sensor nodes which consume energy heavily depending upon the magnitude of data which is transmitted or received by the nodes in the network. In this paper, our primary aim is to reduce the quantity of data transmitted to the data‐collecting sink, which helps in the energy preservation and eventually leads to network longevity. To address this concern, in this paper, we propose a novel framework for energy‐efficient compressive data gathering (NFECG) for heterogeneous WSN. NFECG works in four following phases; in the first phase, the cluster head (CH) selection is performed by considering remaining energy, “distance within the nodes and the sink,” and node density; in second phase, sleep scheduling is done among the cluster member nodes; further, in third phase, the compression of the aggregated data is performed at the CH level, and equivalent compressed sparse signals are generated which are transmitted to sink. In the last phase, at the sink, decompression is applied to retrieve the original signals. The simulation of NFECG is performed using MATLAB under two cases of different network area and number of nodes. We examine its performance for various performance metrics and also inspect for its scalable characteristics. The results show that for one of the two cases, it improves stability period and network lifetime by 52.59% and 46.09%, respectively, as compared to energy‐adjusted high‐level data total tree (EHDT) protocol, and also for the other case of network configuration, it acquires supreme performance.

Understanding bubble and void nucleation in dual ion irradiated T91 steel using single parameter experiments

Ferritic-martensitic steels are attractive candidates for structural materials in next generation nuclear reactor systems due to their resistance to radiation induced swelling. Cavity and dislocation loop evolution was characterized in dual ion irradiated T91 steel in three separate irradiation campaigns examining single parameter dependencies of temperature, helium co-injection rate, and damage rate. Irradiations resulted in bimodal cavity size distributions across nearly all ranges of experimental parameters. It was determined that irradiation temperature and helium co-injection rate are stronger influences on bubble stability and the transition from bubbles to voids than is the irradiation damage rate. At low helium injection rates all helium is in vacancy clusters that evolve into bubbles or voids. At high helium injection rates, bubbles become saturated with helium resulting in accumulation of helium at other traps such as dislocation loops. At intermediate levels of He that should aid in the nucleation of bubbles and enhance swelling, the high density of sinks in the F-M microstructure suppresses bubble nucleation and therefore, the onset of swelling. At high enough temperatures, helium is only in bubbles as other strong helium traps, such as dislocation loops, did not form. The mechanism of bubble to void transition was found to shift from being driven by the accumulation of helium to the critical bubble at low damage rates to being driven by spontaneous formation by stochastic vacancy fluctuation at high damage rates.