Total Number Density Research Articles

Exploring faint white dwarfs and the luminosity function with Subaru HSC and SDSS in Stripe 82

Abstract We present 5,080 white dwarf (WD) candidates selected from stars matching between the multi-band imaging datasets of the Subaru Hyper Suprime-Cam (HSC) Survey and the Sloan Digital Sky Survey (SDSS) in the Stripe82 region covering about 165 deg2. We select WD candidates from the “reduced proper motion” diagram by combining the apparent magnitude in the range i = 19 – 24 and the proper motion measured from the datasets among a baseline of ∼ 14 years. We refine the WD candidates by fitting blackbody and template WD atmosphere models to HSC photometries for each candidate, enabling the estimation of distance and tangential velocity (vt). The deep HSC data allow us to identify low-temperature (<4000 K) and faint WD candidates down to absolute magnitude, Mbol ≃ 17. We evaluate the selection function of our WD candidates using a mock catalogue of spatial and kinematic distributions of WDs in the (thin and thick) disc and halo regions based on a Galactic model. We construct samples of disc and halo WD candidates by selecting WDs with tangential velocity, 40 < vt/[km s−1] < 80 and 200 < vt/[km s−1] < 500, respectively. The total number densities of the disc and halo WDs are (9.33 ± 0.89) × 10−3 pc−3 and (6.34 ± 2.90) × 10−4 pc−3. Our luminosity functions (LF) extend down to fainter absolute magnitudes compared with previous work. The faint WDs could represent the oldest generation of building blocks over the past ∼10 billion years of the assembly history of our Milky Way.

Flare-accelerated Electrons in the Kappa Distribution from X-Ray Spectra with the Warm-target Model

Abstract X-ray observations provide important and valuable insights into the acceleration and propagation of nonthermal electrons during solar flares. Improved X-ray spectral analysis requires a deeper understanding of the dynamics of energetic electrons. Previous studies have demonstrated that the dynamics of accelerated electrons with a few thermal speeds are more complex than those with significantly higher speeds. To better describe the energetic electrons after injection, a model considering energy diffusion and thermalization effects in flare conditions (the warm-target model) has recently been developed for spectral analysis of hard X-rays. This model has demonstrated how the low-energy cutoff, which can hardly be constrained in cold-target modeling, can be determined. However, the power-law form may not be the most suitable representation of injected electrons. The kappa distribution, which is proposed as a physical consequence of electron acceleration, has been applied successfully in RHESSI spectral analysis. In this study, we employ the kappa-form injected electrons in the warm-target model to analyze two M-class flares, observed by RHESSI and the Spectrometer/Telescope for Imaging X-rays, respectively. The best-fit results show that the kappa-form energetic electron spectrum generates lower nonthermal energy than the power-law form when producing a similar photon spectrum in the fit range. We also demonstrated that the fit parameters associated with the kappa-form electron spectrum can be well determined with small uncertainty. Further, the kappa distribution, which covers the entire electron energy range, enables the determination of key electron properties such as total electron number density and average energy at the flare site, providing valuable information on electron acceleration processes.

Effect of Al2O3 and CaO/SiO2 ratio in slag on the cleanliness of bearing steel GCr15

This study investigates the effect of Al2O3 content (ranging from 30% to 38%) and the CaO/SiO2 ratio (ranging from 4 to 7) in LF refining slag at 1600 °C on the cleanliness of bearing steel through laboratory experiments. The driving forces (concentration difference ΔC) of four inclusions (Al2O3, MgO-Al2O3, Mg4Al2O7, and MgO) in the CaO-SiO2-Al2O3-5% MgO slag as well as the slag viscosity (η) at 1600 °C were calculated by Factsage 8.1 software. The relationship between ΔC/η (specifically for MgO·Al2O3 inclusions) and the cleanliness of bearing steel was investigated. The results show that the steel-slag reaction significantly reduces the total oxygen content, inclusion number density, and area fraction within the molten steel, thereby augmenting its cleanliness. With increasing Al2O3 content and CaO/SiO2 ratio in the slag, a notable trend of initial decline followed by subsequent increase is observed in both total oxygen content and total inclusion number density and area fraction within the molten steel. The LF slag composition is suggested to comprise 32% Al2O3, with a CaO/SiO2 ratio of 6. The ΔC/η ratio of MgO·Al2O3 inclusions shows a positive correlation with the apparent rate constant of oxygen removal (ko) while exhibiting a negative correlation with both the number density and area fraction of MgO·Al2O3 inclusions. This indicates that ΔC/η ratio of MgO·Al2O3 inclusions directly affects the removal rate of MgO·Al2O3 inclusions. Moreover, LF refining slag exhibits varying adsorption capacities for the four types of inclusions, ranked as Al2O3 > MgAl2O4 > Mg4Al2O7 > MgO.

The combined effect of pre-aging and Mg/Si ratio on the natural aging and bake hardening in Al-Mg-Si-0.7Cu alloys

The combined influences of pre-aging treatment (PA) and changing Mg/Si ratio on the natural aging (NA) effect and bake hardening response for a series of 6000 series alloys with excess Mg and Cu content was studied. The results showed that PA provides a clear improvement in alloy hardness after paint baking whereas a rising excess Mg (from 1.5 to 3.0) decreases this effect. The hardness in T4P temper however was generally relatively low, due to the combined effect of PA and a high Mg/Si ratio. The strong interaction energy between Cu and Mg was responsible for facilitating the clustering and precipitation processes inducing this behavior. During NA, Mg-Cu and Mg-Mg clusters were found in addition to the Mg-Si(-Cu) clusters, with the total cluster number density decreasing in excess-Mg alloys, resulting in reduced T4P temper hardness. After bake hardening, the disordered β″ precipitates, containing substructures of “low density cylinders” (LDC) and Cu sub-unit clusters, and the lath-like QP2 phases are responsible for the excellent hardening response regardless of Mg/Si ratio effects. The alloy with a Mg/Si ratio of 1.5 exhibits a low strength in T4P temper (134 MP) and very high strength (274 MPa), coupled with a good ductility (14%) after paint baking. This alloy has great potential for automotive application.

Effect of La/Nd ratio on microstructure and tensile properties of AZ91-RE alloys

The effect of La/Nd ratio on the microstructure and tensile properties of AZ91-RE alloys was studied. Typical characterization was performed to analyze the volume fraction, mean nearest neighbor distance (NND), and number density of the secondary phases. First-principles calculations were employed to determine the formation enthalpy, mechanical and thermodynamics properties of the secondary phases. The results demonstrate that the alloy with a mass fraction ratio of La to Nd (wLa/wNd) of 3:2 exhibits the finest average grain size, the smallest mean NND, and the highest total number density of secondary phases. The calculations indicate that the formation of Al11La3 and Al2Nd is energetically favorable. Furthermore, Al11La3 and Al2La display significantly superior deformation resistance, shear deformation resistance, solid stiffness and thermal stability compared to other secondary phases. Therefore, increasing the content of Al11La3 and Al2La phases contributes to improving the mechanical properties of AZ91-RE alloy.

Laboratory study of rotationally inelastic collisions of CO2 at low temperatures.

The rotational relaxation of CO2 by inelastic collisions has been studied in three supersonic jets. The jets were probed by means of Raman spectroscopy with high spectral and spatial resolutions, measuring the rotational populations and the total number density. The time evolution of the rotational populations was analyzed by means of a kinetic master equation, with the help of the energy-corrected sudden power law to relate the numerous state-to-state rate (STS rates) coefficients. In the thermal range investigated, 60-260 K, the STS rates decrease with increasing temperature and with increasing change in the rotational quantum number. Other quantities of interest for fluid dynamics, such as the rotational collision number, the relaxation cross section, and the bulk viscosity, have been derived from the STS rates.

Effect of Relative Humidity on the Rate of New Particle Formation for Different VOCs

Atmospheric new particle formation (NPF) is an important source of aerosol particles and cloud condensation nuclei, which affect both climate and human health. In pristine environments, oxidation of biogenic volatile organic compounds (VOCs) is a major contributor to NPF. However, the impact of relative humidity (RH) on NPF from these precursors remains poorly understood. Herein, we report on NPF, as inferred from measurements of total particle number density with a particle diameter (dp) > 7 nm, from three VOCs (sabinene, α-terpineol, and myrtenol) subjected to dark ozonolysis. From a series of comparative experiments under humid (60% RH) and dry (~0% RH) conditions and a variety of VOC mixing ratios (ξVOC, parts per billion by volume, ppbv), we show varied behavior in NPF at elevated RH depending on the VOC and ξVOC. In general, RH-dependent enhancement of NPF at an ξVOC between <1 ppbv and 20 ppbv was observed for select VOCs. Our results suggest that gaseous water at particle genesis enhances NPF by promoting the formation of low-volatility organic compound gas-phase products (LVOCs). This is supported by measurements of the rate of NPF for α-pinene-derived SOA, where RH had a greater influence on the initial rate of NPF than did ξVOC and ξO3.

Plasma parameters correction method based on plasma image-spectrum fusion for matrix effect elimination in LIBS.

Matrix effect is one of the obstacles that hinders the rapid development of laser-induced breakdown spectroscopy (LIBS), and it is currently a hot, challenging, and focal point in research. To eliminate the matrix effect, this study proposed a plasma parameters correction method based on plasma image-spectrum fusion (PPC-PISF). This method corrects the total number density, plasma temperature, and electron number density variations caused by matrix effect using effective features in plasma images and spectra. To verify the feasibility of this method, experiments were conducted on pressed and metal samples, and the results were compared with those corrected by image-assisted LIBS (IA-LIBS). For the pressed samples, after correction by PPC-PISF, the R2 of the calibration curves all improved to above 0.993, the average root-mean-square error (RMSE) decreased by 41.05%, and the average relative error (ARE) decreased by 59.35% evenly in comparison to IA-LIBS. For the metal samples, after correction by PPC-PISF, the R2 of the calibration curves all increased to above 0.997. Additionally, the RMSE decreased by 29.63% evenly, the average ARE decreased by 38.74% compared to IA-LIBS. The experimental results indicate that this method is an effective method for eliminating the matrix effect, promoting the further development of LIBS in industrial detection.

Coulomb and symmetry-energy effects on proton and neutron density-distributions in central heavy-ion collisions, across beam energies and system masses

In this contribution, we review our current and previous investigations of total, proton, and neutron particle number densities and the asymmetry of proton and neutron density distributions achievable in central heavy-ion collisions at beam energy below 800 MeV/nucleon. Furthermore, the effects of the Coulomb interaction and the dependence on a system size in three representative symmetric and asymmetric Ca, Sn and Pb systems are studied. The Boltzmann-Uhlenbeck-Uehling (pBUU) transport and Time-Dependent Hartree-Fock (TDHF) models, employing the SVbas, SkT3 and SVsym Skyrme interactions, are used in these simulations. We find that (i) the highest total densities predicted at Ebeam = 800 MeV/nucleon are on the order of ∼ 2.5ρ0 (ρ0 = 0.16 fm−3), (ii) the proton-neutron asymmetry for maximal densities, δ = (ρnmax−ρpmax)/(ρnmax+ρpmax) do not generally exceed the asymmetry in the initial state of the collision at all beam energies and tend to decrease during the reaction, and (iii) a significant portion of this asymmetry has its microscopic origin in Coulomb forces, masking the pure nuclear contribution. In addition, the evolution of normalized maximal proton, neutron, and total nucleon number density with increasing beam energy, the impact of correlations in the reaction, and the time evolution of the proton and neutron density distributions in the plane transverse to the beam direction are illustrated and discussed.

Extended total number density compensation for uranium determination by laser-induced breakdown spectroscopy

BackgroundVariations in plasma properties among spectra and samples lead to significant signal uncertainty and matrix effects in laser-induced breakdown spectroscopy (LIBS). To address this issue, direct compensation for plasma property variations is considered highly desirable. However, reliably compensating for the total number density variation is challenging due to inaccurate spectroscopic parameters. For reliable compensation, a total number density compensation (TNDC) method was presented in our recent work, but its applicability is limited to simple samples because of its strict assumptions. In this study, we propose a new pre-processing method, namely extended TNDC (ETNDC), to reduce signal uncertainty and matrix effects in the more complex analytical task of uranium determination. ResultsETNDC reflects the total number density variation with a weighted combination of spectral lines from all major elements and incorporates temperature and electron density compensation into the weighting coefficients. The method is evaluated on yellow cake samples and combined with regression models for uranium determination. Using the typical validation set and line combination, the mean relative standard deviation (RSD) of U II 417.159 nm in validation samples decreases from 4.92% to 2.27%, and the root mean square error of prediction (RMSEP) and the mean RSD of prediction results decrease from 4.81% to 1.93% and from 1.92% to 1.56%, respectively. Furthermore, the results of 10 validation sets and 216 line combinations show that ETNDC outperforms baseline methods in terms of average performance and robustness. SignificanceFor the first time, ETNDC explicitly addresses the temperature and electron density variations while compensating for the total number density variation, where the inaccurate spectroscopic parameters are avoided by fitting related quantities using concentration information. The method demonstrates effective and robust improvement in signal repeatability and analytical performance in uranium determination, facilitating accurate quantification of the LIBS technique.

Effect of Mg Addition on Inclusions in the Welding Heat-Affected Zone of Pressure Vessel Steels

With the development of the pressure vessel industry, high-energy wire welding has a great future. However, this means higher demands on the weldability of pressure vessel steels. Controlling inclusions via oxidative metallurgy is a reliable method of improving the weldability of pressure vessel steels. Hence, in this paper, experimental steels with different Mg element mass fractions were prepared using vacuum metallurgy. Simulated welding for high-heat input welding was carried out using the Gleeble-2000 welding thermal simulation test machine. The inclusions in the welding heat-affected zone (HAZ) in the experimental steels were observed using an optical microscope (OM) and scanning electron microscope (SEM). The compositions of the inclusions were analyzed using an energy-dispersive spectrometer (EDS). The research results indicated that the addition of Mg could increase the number density of the inclusions in the welding HAZ. With the addition of Mg from 0 to 5 wt.%, the total number density of the inclusions increased from 133 to 687 pieces/mm2, and the number density of the inclusions with a size of 0–5 μm2 increased from 122 to 579 pieces/mm2. The inclusions in the experimental steel welding HAZ with Mg elements were mainly elliptical composite inclusions composed of (Mg-Zr-O) + MnS. Moreover, MnS precipitated on the surface of the Mg-containing inclusions in the welding HAZ. Intragranular acicular ferrite (IAF) nucleation was primarily induced via the minimum lattice mismatch mechanism, supplemented with stress-strain energy and inert interface energy mechanisms.

Structural changes in Schwann cells and nerve fibres in type 1 diabetes: relationship with diabetic polyneuropathy

Aims/hypothesisOur aim was to investigate structural changes of cutaneous Schwann cells (SCs), including nociceptive Schwann cells (nSCs) and axons, in individuals with diabetic polyneuropathy. We also aimed to investigate the relationship between these changes and peripheral neuropathic symptoms in type 1 diabetes.MethodsSkin biopsies (3 mm) taken from carefully phenotyped participants with type 1 diabetes without polyneuropathy (T1D, n=25), type 1 diabetes with painless diabetic polyneuropathy (T1DPN, n=30) and type 1 diabetes with painful diabetic polyneuropathy (P-T1DPN, n=27), and from healthy control individuals (n=25) were immunostained with relevant antibodies to visualise SCs and nerve fibres. Stereological methods were used to quantify the expression of cutaneous SCs and nerve fibres.ResultsThere was a difference in the number density of nSCs not abutting to nerve fibres between the groups (p=0.004) but not in the number density of nSCs abutting to nerve fibres, nor in solitary or total subepidermal SC soma number density. The overall dermal SC expression (measured by dermal SC area fraction and subepidermal SC process density) and peripheral nerve fibre expression (measured by intraepidermal nerve fibre density, dermal nerve fibre area fraction and subepidermal nerve fibre density) differed between the groups (all p<0.05): significant differences were seen in participants with T1DPN and P-T1DPN compared with those without diabetic polyneuropathy (healthy control and T1D groups) (all p<0.05). No difference was found between participants in the T1DPN and P-T1DPN group, nor between participants in the T1D and healthy control group (all p>0.05). Correlational analysis showed that cutaneous SC processes and nerve fibres were highly associated, and they were weakly negatively correlated with different neuropathy measures.Conclusions/interpretationCutaneous SC processes and nerves, but not SC soma, are degenerated and interdependent in individuals with diabetic polyneuropathy. However, an increase in structurally damaged nSCs was seen in individuals with diabetic polyneuropathy. Furthermore, dermal SC processes and nerve fibres correlate weakly with clinical measures of neuropathy and may play a partial role in the pathophysiology of diabetic polyneuropathy in type 1 diabetes.Graphical

Evaluation of the Longissimus Thoracis et Lumborum Muscle Quality of Chaka and Tibetan Sheep and the Analysis of Possible Mechanisms Regulating Meat Quality.

This study aimed to comprehensively evaluate the characteristics in the longissimus thoracis et lumborum (LTL) muscle of Chaka (CK) sheep and Tibetan (TB) sheep, and transcriptomics-metabolomics association analysis was used to find the possible genes, differential metabolites, and significant differential metabolic pathways that lead to meat quality differences. Based on the researched results, the nutritional quality of meat, including the contents of ether extract (11.95% vs. 10.56%), unsaturated fatty acid (51.20% vs. 47.69%), and polyunsaturated fatty acid (5.71% vs. 3.97%), were better in TB sheep than in CK sheep, while the CK sheep has better muscle fiber characteristics, such as the total number (62 vs. 45) and muscle fiber density (1426.54 mm2 vs. 1158.77 mm2) and flavor. Omics research has shown that the key differential metabolites and metabolic pathways were dominated by amino acid metabolism, particularly the glutathione metabolism, taurine and hypotaurine metabolism, and lipid metabolism-related pathways, such as glycerophospholipid metabolism and the sphingolipid signaling pathway. The intermediate metabolite sn-Glycerol 3-phosphoethanolamine played a key role in determining sheep meat quality, which was regulated by GPAT2, PLPP2, AGPAT1, PNPLA2, and GPAT4 and correlated with meat color, texture, and flavor. Overall, these results will provide effective information and more evidence to support further exploration of valuable biomarkers of meat quality.

Atomically-informed dislocation dynamics model for prediction of void hardening in irradiated tungsten

Nanometric voids are one of the fundamental defects generated by neutron irradiation in fusion environment, which impede dislocation motion and cause hardening of plasma facing tungsten. Accurate prediction of voids hardening is crucial for safety evaluation of irradiated tungsten. In this paper, we develop a void-dislocation interaction model within the framework of dislocation dynamics (DD) and implement it in open-source DD software ParaDiS. We use this model to study the hardening effects of randomly-distributed voids with different sizes and number densities. The model for short-range interaction during dislocation-void contact, especially the dislocation movement on void surface, is informed and calibrated by atomistic simulations. Meanwhile, the long-range elastic interaction between dislocation and void is efficiently computed by the approach developed in our recent work (Wu et al., 2022) with Eshelby's equivalent inclusion method. Our DD simulations show that the average resistance by voids with various sizes is proportional to the 2/3 power of total number density. We also find that a modified Friedel-Kroupa-Hirsch (MFKH) model can quantify the hardening effects of nanometric voids, where the hardening coefficient depends on an effective average void diameter that accounts for the size distribution of voids. This MFKH model extends our previous work (Wu et al., 2022) that addresses the hardening of small vacancy clusters where dislocations simply cut through them, which is essentially an elastic perturbation to the dislocation dynamics. The proposed MFKH model can predict both small vacancy clusters and nanometric voids hardening effects with only difference in size dependent hardening coefficient. We further verify the MFKH model by comparing its quick predictions of the hardening effects by randomly-distributed nanometric voids with experiments on twelve neutron-irradiated tungsten samples.

Separate and joint clustering characteristics of large-Stokes-number sprays subjected to turbulent co-flows

Separate and joint droplets, clusters, and voids characteristics of sprays injected in a turbulent co-flow are investigated experimentally. Simultaneous Mie scattering and interferometric laser imaging for droplet sizing along with separate hotwire anemometry are performed. The turbulent co-flow characteristics are adjusted using zero, one or two perforated plates. The Taylor-length-scale-based Reynolds number varies from 10 to 38, and the Stokes number estimated based on the Kolmogorov time scale varies from 3 to 25. The results show that the mean length scale of the clusters normalized by the Kolmogorov length scale varies linearly with the Stokes number. However, the mean void length scale is of the order of the integral length scale. It is shown that the number density of the droplets inside the clusters is approximately 7 times larger than that in the voids. The ratios of the droplets number densities in the clusters and voids to the total number density are independent of the test conditions and equal 5.5 and 0.8, respectively. The joint probability density function of the droplets diameter and clusters area shows that the droplets with the most probable diameter are found in the majority of the clusters. It is argued that intensifying the turbulence broadens the range of turbulent eddy size in the co-flow which allows for accommodating droplets with a broad range of diameters in the clusters. The results are of significance for engineering applications that aim to modify the clustering characteristics of large-Stokes-number droplets sprayed into turbulent co-flows.

A Eulerian population balance/Monte Carlo approach for simulating laminar aluminum dust flames

Recently, metal powders have been conceptualized as carbon-free recyclable energy carriers that may form a cornerstone of a sustainable energy economy. The combustion of metal dusts in oxidizing atmospheres is exothermal and yields oxide particles that could, potentially, be retrieved and, subsequently, recharged by conversion to pure metals using green primary energy sources. As a step towards a predictive tool for designing metal dust combustors, we present a fully Eulerian modelling approach for laminar particle-laden reactive flows that is, conceptually, based on a population balance description of the dispersed particles and relies on a stochastic Eulerian solution strategy. While the population balance equation (PBE) is formulated for the number-weighted distribution of characteristic properties among all particles near a spatial location, it is kinetically informed by the rates at which mass, momentum and heat are exchanged between the carrier gas and the particulate phase on the single particle level. Within the scope of the Eulerian Monte Carlo solution scheme, the property distribution is discretely represented in terms of the total number density and a finite number of property samples and the computational work is channelled towards the Eulerian estimation of mean particle properties.For the case of reactive aluminum particles, we combine a kinetic description of the gas-particle heat and mass transfer with a transport-limited continuum formulation to obtain rate expressions that are valid across the entire particle size range from the free molecular through the continuum regime. Besides velocity, the particle properties include only the particle mass, temperature and oxide mass fraction. This set of thermochemical degrees of freedom is retained also as phase transitions due to melting occur, drawing on a smooth blend of the solid and liquid thermodynamic and material properties. The particle-level formulation encompasses aluminum evaporation, surface oxidation, scavenging of oxide smoke, oxide evaporation/dissociation and radiation. After investigating how these effects translate, through the PBE, to the particle population level and affect the combustion in a homogeneous dust reactor, we analyze the combustion of an aluminum dust in a counterflow flame and validate predictions of the particles’ centerline velocity profile and the flame speed by comparison with available experimental data. Concomitantly, nitrogen oxide emissions are investigated along with the particle burnout and outlet size distribution.

Investigation of the signal uncertainty in laser-induced breakdown spectroscopy based on error propagation considering self-absorption

The relatively high signal uncertainty of laser-induced breakdown spectroscopy (LIBS) is a key obstacle to its analytical performance and large-scale application. Despite the extensive research efforts to reduce signal uncertainty, few fundamental studies have been conducted because of the complexity of the microscopic mechanisms involved in plasma evolution. Recently, error propagation analysis has provided an inspiring perspective by linking signal uncertainty with plasma property fluctuations, while further investigation is urgently needed due to the limitations of the employed plasma diagnostic techniques. In this study, a spectrum fitting model was proposed for optically thick and homogeneous plasmas to provide more reliable plasma properties for error propagation analysis for the first time. The model was applied to laser-induced copper plasmas using a laser wavelength of 1064 nm and a pulse duration of 25 ns. The uncertainty of an atomic copper line was analyzed at different delay times. Our findings revealed that the fluctuation of columnar total number density was the most significant factor under the investigated conditions, and that the correlation term of temperature and columnar total number density made a considerable negative contribution. Furthermore, self-absorption suppressed the magnitudes of major contribution terms for the signal uncertainty of LIBS.

Effect of cooling rate on non-metallic inclusion formation and precipitation and micro-segregation of Mn and Al in Fe–23Mn–10Al–0.7C steel

The present study assesses the influence of the cooling rate on the morphology, composition, number density, size distribution of inclusions, and microsegregation of elements in Fe–23Mn–10Al–0.7 steel. The results indicate that with the increase of cooling rate from 5.1 K/s to 14.51 K/s, the total number density of inclusions increases from 28 mm−2 to 32 mm−2, with no change in the type of inclusions, the average size of MnS inclusion decreases from 9.57 μm to 5.21 μm. The precipitation and growth of MnS inclusion are predicted according to the coupled model, matching well with the experimental results. Furthermore, it is observed that AlN inclusion formed in the liquid steel can float up to the surface of the liquid steel, reducing the dissolved nitrogen content in the steel. As the cooling rate increases, the size and density of AlN inclusions on the liquid steel surface decrease. Combining the lattice mismatch of inclusions and the pushing and engulfment behavior of inclusions, the effect of cooling rate on the MnS precipitation for Al2O3 and AlN is analyzed. Moreover, under different cooling rates, Al segregation is very remarkable and it is low in interdendritic regions but high in dendrite stems.

MMS observation of cold electrons in the magnetotail reconnection separatrix region

Cold plasmas can modify dynamical processes during magnetic reconnection. There are many studies on the roles of cold ions in modifying reconnection process. However, there have been a lack of studies on the roles of cold electrons. Using MMS high-cadence data, we present observation of cold electrons originated from the terrestrial lobe at the magnetotail reconnection separatrix region. The number density of these cold electrons relative to the total number density was 67%∼95%. Current density carried by them can reach −50nA/m2, which is comparable to or even greater than that of current driven by other electron populations. Currents driven by cold and high-energy electrons generally canceled each other out. These findings indicate that cold electrons can greatly modify the current at the separatrix. Currents driven by cold electrons are stronger in the inner part of the separatrix region, and have electron-scale structures, where current density changes by ∼ 20nA/m2 in ∼ 3 de. Our observations provide insights into roles of cold electrons during reconnection and electron dynamics in reconnection jet far downstream of the X-line.

In-situ synchrotron X-ray radiography study of primary Fe-rich phases growth in Al-Fe( Cu) alloys

Plate-like iron-rich intermetallic phases (Fe-rich phases) greatly decrease the elongation and fatigue strength of recycled Al alloys. The alloy composition and the manufacturing process parameters influence the type, and shape of Fe-rich phases. In this study, the influence of the cooling rate (0.1, 0.5, and 1.0 °C/s) on the nucleation and growth of primary Fe-rich phases during solidification of Al-Fe(Cu) alloy has been quantified by synchrotron X-ray radiography. The Kikuchi patterns and deep-etched methods showed that rod-shape and plate-like primary Al3Fe phases are present in the studied alloy. The in-situ experimental results indicate that the total number and number density of primary Fe-rich phases in AlFe alloys is very similar at cooling rates of 0.1 °C/s and 1.0 °C/s but increases a 300 % at cooling rate of 0.5 °C/s. The nucleation rate of Al3Fe in AlFe alloys at three cooling rates (0.1, 0.5, and 1.0 °C/s) are 15.5, 44.0, 25.0 No./s, respectively. These decrements are due to alloy compositions are very closed to the eutectic composition (about 1.8% Fe), the less time for them to form primary Fe-rich phases at high cooling rate of 1.0 °C/s. The variation trend of total number, number density, and nucleation rate of primary Al3Fe phases in Al-Cu-Fe alloys is similar to those of in AlFe alloys. The maximum length of typical Al3Fe phases in AlFe alloys decrease from 845 μm to 222 μm as the cooling rate increased. This is because that higher cooling rate resulting in less diffusion time for limiting Fe atoms diffusion, also inhibiting them grow into large plates. The combined Cu addition and higher cooling rate resulting in the constitutional undercooling, and finally promote the formation of refined primary Al3Fe particles.