Equilibrium Volume Research Articles

Coarsening of solidβ-Sn particles in liquid Pb-Sn alloys: Reinterpretation of experimental data in the framework of trans-interface-diffusion-controlled coarsening

Previously published data, not ours, on the coarsening of solid \ensuremath{\beta}-Sn particles in a liquid Pb-Sn matrix of near-eutectic composition are reanalyzed within the framework of the trans-interface-diffusion-controlled (TIDC) theory of coarsening. The data were obtained under conditions of microgravity from specimens heat-treated at 458 K and containing four equilibrium volume fractions ${f}_{e}$ equaling 0.10, 0.15, 0.20, and 0.30. We show that the rate constants $k({f}_{e})$ in the traditional coarsening equation ${\ensuremath{\langle}r\ensuremath{\rangle}}^{3}\ensuremath{\approx}k({f}_{e})t$ for the kinetics of growth of the average particle radius $\ensuremath{\langle}r\ensuremath{\rangle}$ are nearly independent of ${f}_{e}$, in disagreement with numerous theories wherein coarsening is controlled by diffusion in the host matrix phase. Atom transport in TIDC coarsening is instead controlled by slow diffusion through the diffuse interface, of width \ensuremath{\delta}, separating the dispersed particles from the matrix; the kinetics of this process is independent of ${f}_{e}$. Atomistic simulations were performed to estimate the properties of the solid-liquid (S-L) interface at 458 K, 2 K above the Pb-Sn eutectic temperature. The S-L interfaces normal to (001) and (010) of tetragonal \ensuremath{\beta}-Sn were examined and found to have nearly identical properties, including interface widths of \ensuremath{\sim}1.7 nm. In conjunction with the diffusivities in solid \ensuremath{\beta}-Sn and liquid hypereutectic Pb-Sn at 458 K, we estimate that TIDC coarsening should prevail for solid Sn particles \ensuremath{\sim}1700 \ensuremath{\mu}m in radius, far exceeding the maximum radius of \ensuremath{\sim}100 \ensuremath{\mu}m measured experimentally. The TIDC theory also predicts that the kinetics of growth obeys the equation ${\ensuremath{\langle}r\ensuremath{\rangle}}^{n}\ensuremath{\propto}t$. The temporal exponent $n$ was evaluated to be \ensuremath{\sim}2.5, as ascertained by analyzing data on the particle size distributions (PSDs; histograms) for the alloys with ${f}_{e}=0.15$, 0.20, and 0.30. The histograms were converted to experimental cumulative distribution functions (ECDFs) and analyzed using the Kolmogorov-Smirnov (K-S) test applied to the theoretical CDFs predicted by the TIDC theory. We report the first successful application of the K-S test to experimental PSDs concomitant with particle coarsening. From every aspect of the experimental data amenable to analysis, we conclude that the coarsening behavior of solid Sn particles in liquid hypereutectic Pb-Sn alloys is fully consistent with the predictions of the TIDC theory of coarsening.

Accurate Deep Potential model for the Al–Cu–Mg alloy in the full concentration space* *Project supported by the National Natural Science Foundation of China (Grant No. 11871110), the National Key Research and Development Program of China (Grant Nos. 2016YFB0201200 and 2016YFB0201203), and Beijing Academy of Artificial Intelligence (BAAI).

Combining first-principles accuracy and empirical-potential efficiency for the description of the potential energy surface (PES) is the philosopher’s stone for unraveling the nature of matter via atomistic simulation. This has been particularly challenging for multi-component alloy systems due to the complex and non-linear nature of the associated PES. In this work, we develop an accurate PES model for the Al–Cu–Mg system by employing deep potential (DP), a neural network based representation of the PES, and DP generator (DP-GEN), a concurrent-learning scheme that generates a compact set of ab initio data for training. The resulting DP model gives predictions consistent with first-principles calculations for various binary and ternary systems on their fundamental energetic and mechanical properties, including formation energy, equilibrium volume, equation of state, interstitial energy, vacancy and surface formation energy, as well as elastic moduli. Extensive benchmark shows that the DP model is ready and will be useful for atomistic modeling of the Al–Cu–Mg system within the full range of concentration.

Mechanisms of Ti[formula omitted]Al precipitation in hcp [formula omitted]-Ti

Nucleation and growth of Ti3Al α2 ordered domains in α-Ti–Al–X alloys were characterised using a combination of transmission electron microscopy, atom probe tomography and small angle X-ray scattering. Model alloys based on Ti–7Al (wt.%) and containing O, V and Mo were aged at 550∘C for times up to 120d and the resulting precipitate dispersions were observed at intermediate points. Precipitates grew to around 30nm in size, with a volume fraction of 6–10% depending on tertiary solutes. Interstitial O was found to increase the equilibrium volume fraction of α2, while V and Mo showed relatively little influence. Addition of any of the solutes in this study, but most prominently Mo, was found to increase nucleation density and decrease precipitate size and possibly coarsening rate. Coarsening can be described by the Lifshitz-Slyozov-Wagner model, suggesting a matrix diffusion-controlled coarsening mechanism (rather than control by interfacial coherency). Solutionising temperature was found to affect nucleation number density with an activation energy of Ef=1.5±0.4 eV, supporting the hypothesis that vacancy concentration affects α2 nucleation. The observation that all solutes increase nucleation number density is also consistent with a vacancy-controlled nucleation mechanism.

On an efficient time scheme based on a new mathematical representation of thermodynamic equilibrium for multiphase compositional Darcy flows in porous media

This paper presents a new mathematical representation of multiphase thermodynamic equilibrium using so-called repartition coefficients. Combined with a global mass formulation of multiphase Darcy flow in porous media, it allows the derivation of a computationally efficient family of time schemes. The model accounts for the mass conservation of an arbitrary number of components flowing through an arbitrary number of phases, coupled with thermodynamic equilibrium and pore volume conservation. By separating the thermodynamic equilibrium part from the flow part through the repartition coefficients, the formulation removes the need for any specific handling of phase appearance and disappearance within the flow solver. Any “black box” thermodynamic equilibrium solver can then be used to compute the repartition coefficients, from EOS based solvers to tabulated representation of the thermodynamic equilibrium, each specific choice of thermodynamic solver leading to a new scheme. Three numerical experiments, from a simple beam to a real case, illustrate the good behavior of the approach.

Effect of Ti/V ratio on thermodynamics and kinetics of MC in γ/α matrices of Ti–V microalloyed steels

Through the solubility product theory of the ternary secondary phase, classical nucleation theory, and Ostwald ripening theory, a model was established to describe the thermodynamics and kinetics of (Ti, V)C precipitates in austenite/ferrite (γ/α) matrices. The model was used to calculate the volume fraction, precipitation–temperature–time (PTT) curve, and nucleation rate–temperature (NrT) curve of MC (M = Ti, V) precipitates in γ/α matrices in Ti–V microalloyed steels with various Ti/V ratios, which is verified by hardness tester, transmission electron microscopy and energy-dispersive X-ray spectroscopy. The calculations indicate that, by decreasing Ti/V ratio from Ti4V0 steel to Ti0V4 steel, the complete-dissolution temperature decreases monotonically from 1226 to 830 °C, and the equilibrium volume fraction of MC precipitated from austenite decreases from 0.333% to 0.091% at 900 °C. Moreover, the maximum nucleation temperature of MC precipitated from α matrix decreases from 748 to 605 °C and the fastest precipitation temperature decreases from 844 to 675 °C as Ti/V ratio decreases. PTT and NrT diagrams of MC precipitated from α matrices in different Ti–V microalloyed steels all exhibit C-shaped and inverse C-shaped curves. In addition, both theoretical calculation and experimental results show that when tempered at 600 °C for 100 h, Ti2V2 steel shows the largest hardness value of 312 HV among the three steels tested because it has a larger volume fraction (0.364%), a larger precipitate density (1689 μm−2), and the smallest average size (8.4 nm) of (Ti, V)C precipitates. The theoretical calculations are consistent with experimental results, which indicates that the thermodynamics and kinetics model for (Ti, V)C precipitates is reliable and accurate.

Controls on the scales of equilibrium during granulite facies metamorphism

AbstractPhase equilibrium modelling is commonly employed to constrain the pressure–temperature (P–T) evolution of granulite facies rocks, from which their geodynamic setting may be inferred. However, defining a suitable equilibrium volume in such rocks is non‐trivial due to heterogeneities in protolith composition and open system behaviour, including melt loss or gain and deformation. Consequently, equilibrium volumes and the mineral assemblages they contain may vary both temporally and spatially within a single rock. Additionally, despite the extreme temperatures they attained, granulites commonly contain microtextures indicating gradients in chemical potential after the metamorphic peak. This study assesses the processes that control compositional heterogeneity between equilibrium volumes in a suprasolidus granulite and the consequences for the development of a range of microstructures. An approach combining phase equilibrium forward modelling and chemical potential diagrams is used to simulate the suprasolidus evolution of two adjacent equilibrium volumes in an Mg‐rich metapelite. Assuming equilibrium within the two compositional domains, evolving granulite facies assemblages vary along a high T/P (125°C/kbar) clockwise P–T path representative of high T/P metamorphic terranes. Many retrograde microtextures in metapelitic rocks can be reproduced by considering chemical potential (µ) gradients in µMgO, µFeO and µCaO between phases, assuming (a) the presence of melt on grain boundaries, (b) that Al2O3 is perfectly immobile and (c) that K2O and Na2O are perfectly mobile. Additionally, documented microtextures in granulites imply local SiO2‐undersaturation, despite the presence of matrix quartz in the rock. Preserving such chemical potential gradients requires that solid phases are chemically and physically isolated from melt. Efficient prograde melt drainage may lead to a loss in melt interconnectivity at high temperature (>900°C), meaning that equilibration of centimetre‐scale compositional domains is controlled by solid‐state diffusion. The presence of isolated pockets of viscous melt allows the formation of discontinuous intergranular reaction microtextures.

Theoretical investigation of the electronic structure, elastic, dynamic properties of intermetallic compound NiBe under pressure

From the beryllide group, NiBe is a hybrid material of CsCl (B2) type structure and presents a large range of stoichiometry. In this paper, we have studied the structural, electronic, elastic, and dynamic properties of NiBe intermetallic compound under pressure by performing ab initio density functional theory using the Cambridge Serial Total Energy Package (CASTEP). In B2 structure, we have obtained the lattice constant ( $${A}_{\mathrm {0}}$$ ), equilibrium volume ( $${V}_{\mathrm {0}}$$ ), bulk modulus ( $${B}_{\mathrm {0}}$$ ) and its pressure derivative ( $${B}_{0}$$ ’) and elastic constants. We have quantitatively analyzed the band structure and the corresponding density of states (DOS). We have also estimated the mechanical stability and brittle/ductile behaviors of this compound based on the computed elastic constants. It is found that this structure is stable between 0 and 50 GPa pressure for NiBe compound. Finally, the changing degree of anisotropy with pressure was analyzed in three and two dimensions.

The determination of radon volumetric activity in atmospheric air and in soil of samarkand and navoi regions

This article presents the results of a study of the concentration and specific activity of various 222 220 radionuclides, such as- Rn, Tn and their variations in the form of the exposure dose rate-EDR, equivalent equilibrium volume activity of radon -EEVAR, long-lived alpha nuclides-LAN in the atmospheric air of the Samarkand and Navoi regions.

Assessment of the radiation situation and distribution of radionuclides in the air of the uranium protoxide-oxide calcination shop

The exposure dose rates, the equivalent equilibrium volume activity of radon, and the activity of long-lived alpha-nuclides in the air of the uranium protoxide-oxide calcination shop were determined. Annual effective doses for workers were calculated. Through the use of nuclear-based polietilentereftalata and chemical filters, the disperse composition of particles in the air was studied. The effectiveness of filters in sampling was evaluated for the uranium content. The kinetics of distribution of uranium in various fractions was studied. The quality coefficients of filters that accumulate uranium relative to its norm in various working places of the shop were estimated.

Ab initio molecular dynamics investigation of point defects in [formula omitted]-U

Uranium (U) is often alloyed with molybdenum (Mo) or zirconium (Zr) in order to stabilize the high-temperature body-centered cubic γ phase of uranium for use in nuclear reactors. However, relatively little experimental or computational investigation has centered on γ-U, largely due to the mechanical instability of this phase at room temperature. This is particularly problematic for density functional theory calculations that typically investigate 0 K properties. However, ab initio molecular dynamics (AIMD) allows for quantum mechanical-based calculations to be performed at non-zero temperatures. In this work, AIMD simulations are performed to calculate the equilibrium volume for the γ phase of U from 900 K to 1400 K. Utilizing the volume at each temperature, the bulk modulus, the radial distribution function, the interstitial and vacancy formation energies, and the diffusion coefficients are determined.

Dominant effect of anharmonicity on the equation of state and thermal conductivity of MgO under extreme conditions

Understanding heat transfer in the earth mantle region is of great scientific interest but highly challenging due to dissimilar conditions from our daily lives. Thermal conductivity of highly pressured and thermally activated materials can be completely different from that at ambient condition. In this study we calculate the equation of state and thermal conductivity of cubic crystalline MgO, a major component of the mantle, in such an environment. It is shown that the material properties are not accurately captured unless rigorous treatment of anharmonicity of phonon vibrational motion is explicitly applied. To predict renormalized phonon dispersion relations, interatomic force constants of high-order expansion are required, especially at elevated temperature. The anharmonicity plays an increasingly substantial role for regulating volume expansion as temperature rises, because the Gibbs free energy of MgO considerably deviates from what was predicted by the quasiharmonic approximation. We find that the lattice thermal conductivity of MgO and the heat transfer of the earth's mantle are reliably estimated only when both the temperature-dependent renormalization of phonon frequencies and four-phonon scattering effects are taken into consideration. We map the characteristics at Geotherm into contour diagrams in which equilibrium volumes and the thermal conductivities are described as functions of temperature and pressure. The thermal conductivity values of MgO in this study are smaller than those in previous theoretical studies due to the additional incorporation of four-phonon scatterings in the calculations. Specifically, deviation between the values in previous studies and in this study becomes larger as thermodynamic variables reach those near the core-mantle boundary. For instance, thermal conductivities of 52.15 and 23.67 $\phantom{\rule{0.16em}{0ex}}{\mathrm{Wm}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ are estimated at ambient and extreme conditions ($T=4000\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and $P=135\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$), respectively.

Insights into the model of non-perfect osmometer cells for cryopreservation: A parametric sweep analysis

Recently, a mathematical model able to describe the non-perfect osmotic behavior of cells during cryopreservation was proposed. The model improves the two-parameter formalism typically adopted in cryopreservation literature by allowing the transmembrane permeation of ions/salt, through the temporary opening of mechanosensitive channels whenever membrane stretching occurs: cells can reach an equilibrium volume different from the initial one, when isotonic conditions are re-established after contacting with impermeant or permeant solutes, such as sucrose or a cryoprotectant agent like dimethyl sulfoxide, respectively.Although the model was conceived as a conservative development of the two-parameter formalism to avoid over-parameterization, a complex picture of the system emerges. To describe this, first an appropriate non-dimensional version of the model equations is derived. Then, a parametric sweep analysis is performed and discussed to highlight the features of the novel model in comparison with the two-parameter formalism: the conditions by which the first reduces to the second are identified. Only equilibrium equations with impermeant sucrose may be analytically derived from the model: their validity is here extended much more than originally assumed. When permeant dimethyl sulfoxide comes into play, the temporary opening of mechanosensitive channels is difficult to predict and prevents the derivation of the equilibrium equations: in this case, a numerical integration of system dynamics up to steady state is required to determine the cell volume at equilibrium. In conclusion, cell volume at equilibrium depends on the position of the temporal window of mechanosensitive channels opening, which, in general, is a complex function of model parameters and operating conditions.

Critical assessment of Co-Cu phase diagram from first-principles calculations

Using first-principles alloy theory, we perform a systematic study of the Co-Cu phase diagram. Calculations are carried out for ferromagnetic and paramagnetic ${\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Cu}}_{x}$ solid solutions with face-centered-cubic (fcc) crystal structure. We find that the equilibrium volumes and magnetic states are crucial for a quantitative description of the thermodynamics of the Co-Cu system at temperatures up to 1400 K. In particular, the paramagnetic state of Cu-rich alloys with persisting local magnetic moments is shown to be responsible for the solubility of a small amount of Co in fcc Cu whereas the excess entropy in the ferromagnetic Co-rich region critically depends on the adopted lattice parameters. None of the common local or semilocal density functional theory approximations have the necessary accuracy for the lattice parameters when compared to the experimental data. The predicted ab initio Co-Cu phase diagram is in good agreement with the measurements and CALPHAD data, making it possible to gain a deep insight into the various contributions to the Gibbs free energy. The present study provides an atomic-level description of the thermodynamic quantities controlling the limited mutual solubility of Co and Cu and highlights the importance of high-temperature magnetism.

Structural and Thermodynamic Properties of the High-Entropy Alloy AlCoCrFeNi Based on First-Principles Calculations

During the past two decades, the high-entropy alloy AlCoCrFeNi has attracted much attention due to its outstanding thermal and mechanical properties under ambient conditions. However, the exploration on the thermodynamic properties of this alloy under high temperatures and high pressures is relatively insufficient. Combining structural modeling with the similar atomic environment (SAE) method and first-principles simulations with the modified mean-field potential (MMFP) approach, we studied the lattice and magnetic structure as well as the thermodynamic properties of the body-centered-cubic AlCoCrFeNi, through supercell simulations. AlCoCrFeNi was found to display a strong local lattice distortion compared with typical 3d high-entropy alloys; the ferromagnetic structure stable at 0 K was predicted to transform to the paramagnetic structure at the Curie temperature TC = 279.75 K, in good agreement with previous calculations; the calculated equilibrium volumes, bulk modulus, and shock Hugoniot all agree well with available experimental data and other theoretical values. These results demonstrate the validity and reliability of our methods used to study the dynamic properties of AlCoCrFeNi, providing a promising scheme for accessing the dynamic properties of sophisticated high-entropy alloys.

Ab Initio Investigations of the Structural, Electronic, Magnetic, and Thermal Properties of Cr2TaGe1-xSnx Quaternary Heusler Alloys

The first-principle calculations were performed in the framework of the density functional theory (DFT) using FP-LAPW method as implemented in Wien2k code to determine the structural stability, electronic, and magnetic properties of quaternary Heusler alloys Cr2TaGe1-xSnx (x = 0, 0.25, 0.50, 0.75, 1.00), The results showed that for the compounds, the AlCu2Mnl-type structure is energetically more stable than CuHg2Ti-type structure at the equilibrium volume. The calculated lattice constants for Cr2TaGe and Cr2TaSn are 6.081 A and 6.311 A, respectively. For mechanical properties, shear modulus, Young’s modulus, elastic constants, Poisson’s ratio and shear anisotropy factor have studied. Their obtained values reveal that these compounds are mechanically stable. The electronic band structures and density of states of our compounds show a half metallic character with total magnetic moments, − 3.00 μB per formula unit with indirect band gap, 0.569 eV and 0.482 eV for Cr2TaGe and Cr2TaSn respectively. Regarding thermal properties such as the thermal expansion coefficient, heat capacity, and Debye temperature, we have applied a very suitable model for studying thermodynamics quantities called the quasi-harmonic Debye model. On the basis of these results, these alloys are predicted to be good candidates for future spintronic applications.

Beyond two-center tight binding: Models for Mg and Zr

We describe a systematic approach to building ab initio tight-binding models and apply this to hexagonal metals Mg and Zr. Our models contain three approximations to plane-wave density functional theory (DFT): (i) we use a small basis set, (ii) we approximate self-consistency, and (iii) we approximate many-center exchange and correlation effects. We test a range of approximations for many-center exchange-correlation and self-consistency to gauge the accuracy of each in isolation. This systematic approach also allows us to combine multiple approximations in the optimal manner for our final tight-binding models. Furthermore, the breakdown of errors into those from individual approximations is expected to be a useful guide for which approximations to include in other tight-binding models. We attempt to correct any remaining errors in our models by fitting a pair potential. Our final tight-binding model for Mg shows excellent agreement with plane-wave results for a wide range of properties (e.g., errors below 10% for self-interstitial formation energies and below 3% for equilibrium volumes) and is expected to be highly transferable due to the minimal amount of fitting. Calculations with our Zr model also show good agreement with plane-wave results (e.g., errors below 2% for equilibrium volumes) except for properties where self-consistency is important, such as self-interstitial formation energies. However, for these properties we are able to generate a tight-binding model which shows excellent agreement with non-self-consistent DFT with a small basis set (i.e., many-center effects are captured accurately by our approximations). As we understand the source of remaining errors in our Zr model we are able to outline the methods required to build upon it to describe the remaining properties with greater accuracy.

Predictions on structural, electronic, magnetic and thermal properties of new Heusler alloys Cr$$_{{{2}}}$$NbSi$$_{{1-x}}$$Ge$$_{{x }}$$ from first-principles calculations

In this study, by using full-potential linearised augmented plane wave (FP-LAPW) method with the generalised gradient approximation (GGA) based on density functional theory (DFT), the structural, electronic, elastic and magnetic properties of the Heusler alloys Cr $$_{\mathrm {2}}$$ NbSi $$_{{1-x}}$$ Ge $$_{x}$$ have been evaluated. The AlCu $$_{\mathrm {2}}$$ Mnl-type structure is more stable than the CuHg $$_{\mathrm {2}}$$ Ti-type structure at equilibrium volume for the compounds. The ground-state properties of our alloys including the lattice parameter and bulk modulus were calculated. In view of Poisson’s and Pugh’s ratio, the ductility and brittleness of Cr $$_{\mathrm {2}}$$ NbSi $$_{{1-x}}$$ Ge $$_{x}$$ has been analysed. The mechanical stability is maintained throughout the pressure range with high value of Debye temperature. The electronic band structures and density of states of our compounds show a half metallic character with total magnetic moments, −3.00 $${\mu }_{\mathrm {B}}$$ per formula unit with indirect band gap, $$E_\mathrm{g}$$ $$=$$ 0.152 eV and 0.262 eV for Cr $$_{\mathrm {2}}$$ NbSi and Cr $$_{\mathrm {2}}$$ NbGe respectively. Furthermore, we have analysed the thermal properties by the quasi-harmonic Debye model. Through the obtained results, we can say that these compounds can be strong candidates for future spintronic applications.

The influence of temperature on the elastic properties of body-centered cubic reduced activation steels

A first-principles based modeling approach to the effect of temperature on the isothermal single-crystal and polycrystalline elastic parameters of Fe-rich solid solutions is reported. The approach integrates alloy theory for chemical and magnetic disorders with accessible experimental data for the equilibrium volume and ferromagnetic phase transition, and is adopted to predict the temperature-dependent elastic parameters of the body-centered cubic phase of three reduced activation steels, CLAM/CLF-1, F82H, EUROFER97, considered as high-temperature material in power reactors. The predictions are assessed based on available experimental data for a reduced activation steel and both experimental and theoretical data for pure Fe. Alloying effects on the elastic constants relative to pure Fe are found to differ in the magnetically ordered and disordered phases. Contributions due to loss of long-range magnetic order, volume expansion, and entropy are important in determining the temperature dependence of the elastic parameters in all investigated materials. A previously reported, peculiar magneto-volume phenomenon on the equation of state in pure Fe is gradually removed by alloying and magnetic disordering, which requires particular attention when describing the thermo-chemical effects derived from the equation of state in Fe-rich solid solutions.

Site-specific concentration of uranium in urine of workers of the hydrometallurgical plant of Stepnogorsk mining and chemical combine.

Radiation monitoring is an important radiation safety measure implemented at the hydrometallurgical plant of the Stepnogorsk mining and chemical combine (HMP SMCC, Republic of Kazakhstan). Follow-up of the workers and their regular medical examinations has laid the basis to create a cohort with the potential to be used in radiation epidemiology. The aim of current pilot study was to analyze the dose forming factors for workers of HMP SMCC. For this, bioassays samples collected from 54 workers employed at eight HMP workshops were measured using the "Agilent 7800 ICP-MS" mass spectrometer. Three years later, measurements were repeated for four workers with the highest concentrations of uranium in urine. The results of site-specific measurements of dose rates, long-lived alpha-particle activity concentrations and equivalent equilibrium volume activity of radon were derived from the archive of the HMP SMCC Service of Radiation and Toxic Safety and analyzed to fully evaluate the radiation situation at those workplaces. Maximum urine uranium concentrations were measured for workers at the extraction workshop and mechanical repair shop (up to 26.7µg/L and 14.6µg/L, respectively). Urinary uranium from workers employed at other sites was mainly (for about 72% of the samples) in the range of values that may occur in natural conditions (< 0.4µg/L). A wide individual variability in uranium concentration in urine samples (from 60% to 200% of CV) was found. A linear dependence of cumulative effective dose on work experience was found with a slope of 7.5mSv per year. This slope did not depend on working place. For the investigated workers, cumulative effective doses of workers were found in the range of low (< 100mSv) and medium doses (100-500mSv). It is concluded that the newly created cohort of HMP SMCC workers has the potential to improve the knowledge on health effects from low- and medium doses of ionizing radiation.

First-Principles Study of the New Half-Metallic Ferromagnetic Quaternary-Heusler Alloys NaXNO (X=Ca, Sr, Ba)

The first-principles approach based on density functional theory (DFT) and the full-potential linearized augmented plane-wave method were employed to investigate the structural, elastic, electronic and magnetic properties of Na[Formula: see text]NO ([Formula: see text], Sr and Ba) quaternary half-Heusler alloys. The generalized gradient approximation (GGA) as parameterized by Perdew, Burke and Ernzerhof (PBE) and the modified Becke–Johnson exchange potential were used. As far as we know, we present our results which for the first time quantitatively account for the electronic structures and magnetic properties of Na[Formula: see text]NO ([Formula: see text], Sr and Ba) quaternary half-Heusler alloys. From the total energy calculation using three possible atomic configurations ([Formula: see text], [Formula: see text] and [Formula: see text]), it is found that the Na[Formula: see text]NO ([Formula: see text], Sr and Ba) quaternary half-Heusler alloys are more stable in the ferromagnetic [Formula: see text]-phase. From our estimated elastic constants [Formula: see text], it is found that all the considered Heusler alloys are mechanically stable in the [Formula: see text]-phase. We have also investigated the robustness of the half-metallicity with respect to the variation of lattice constants in these alloys. We have found that these alloys are half-metallic ferromagnets (HMFs) with a magnetic moment of 2[Formula: see text][Formula: see text] per formula unit at their equilibrium volumes. The spin-polarized electronic band structure and density of states of these quaternary half-Heusler alloys calculated by GGA (mBJ-GGA) show that the minority spin channels have metallic nature and the majority spin channels have a semiconductor character with half-metallic gaps of 0.49[Formula: see text]eV (2.17[Formula: see text]eV), 0.72[Formula: see text]eV (2.28[Formula: see text]eV) and 0.96[Formula: see text]eV (2.22[Formula: see text]eV) for NaCaNO, NaSrNO and NaBaNO quaternary half-Heusler alloys, respectively. Analysis of the density of states and the spin charge density of these quaternary alloys indicates that their magnetic moments mainly originate from the strong spin-polarization of 2[Formula: see text] states of N atoms and O atoms.