Equilibrium Volume Research Articles

A thermodynamic model of phase transition of poly(N-isopropylacrylamide) hydrogels in ionic solutions

Submerged in an aqueous solution of sodium chloride (NaCl), a poly(N-isopropylacrylamide) (PNIPAM) hydrogel can be in one of two phases: swollen phase and collapsed phase. We measure the equilibrium volume of the hydrogel as a function of temperature T and ionic concentration y. The hydrogel is in the swollen phase when T and y are low, and is in the collapsed phase when T and y are high. We develop a thermodynamic model in which the free energy is a function of volume, temperature, and ionic concentration. The free energy also contains several adjustable parameters, which we best-fit to the experimental data of volume as a function of T and y. For a given pair of T and y, the free energy is a function of volume. This function has a single minimum for some pairs of (T, y), but two minima and a maximum for other pairs of (T, y). In the former, the single minimum corresponds to either a swollen or a collapsed state. In the latter, the lower minimum corresponds to a state of equilibrium, the higher minimum corresponds to a metastable state, and the maximum corresponds to an unstable state. When the two minima are equal, the hydrogel undergoes phase transition. The condition of phase transition is represented as a curve on the (T, y) plane. The thermodynamic model represents the experimental data well.

Ab initio исследования влияния давления на структуру, электронные и упругие свойства карбонатов щелочных--щелочно-земельных металлов

Density functional theory with a gradient PBE functional and dispersion correction D3(BJ) in the basis of localized orbitals of the CRYSTAL17 package was used to study the effect of pressure on the structural, electronic, and elastic properties of K2Ca(CO3)2, K2Mg(CO3)2, Na2Ca2(CO3)3, Na2Mg(CO3)2. The parameters of the third-order Birch-Murnaghan equation of state are determined, and it is shown that the equilibrium volume and compressibility modulus depend linearly on the average cation radius. Under pressure, the widths of the upper valence bands increase maximally in K2Ca(CO3)2 and minimally in Na2Ca2(CO3)3, while the centers of gravity of the cationic states shift by ~0.2 eV. Elastic constants and polycrystalline moduli are calculated, which increase with decreasing average cation radius. The shear modulus for K2Ca(CO3)2 and K2Mg(CO3)2 decreases with increasing pressure, and this leads to anomalous behavior of the longitudinal and transverse acoustic wave velocities.

Ab initio studies of the effect of pressure on the structure, electronic and elastic properties of carbonates of alkali-alkaline earth metals

Density functional theory with a gradient PBE functional and dispersion correction D3(BJ) in the basis of localized orbitals of the CRYSTAL17 package was used to study the effect of pressure on the structural, electronic, and elastic properties of K2Ca(CO3)2, K2Mg(CO3)2, Na2Ca2(CO3)3, Na2Mg(CO3)2. The parameters of the third-order Birch--Murnaghan equation of state are determined, and it is shown that the equilibrium volume and compressibility modulus depend linearly on the average cation radius. Under pressure, the widths of the upper valence bands increase maximally in K2Ca(CO3)2 and minimally in Na2Ca2(CO3)3, while the centers of gravity of the cationic states shift by ~0.2 eV. Elastic constants and polycrystalline moduli are calculated, which increase with decreasing average cation radius. The shear modulus for K2Ca(CO3)2 and K2Mg(CO3)2 decreases with increasing pressure, and this leads to anomalous behavior of the longitudinal and transverse acoustic wave velocities. Keywords: ab initio calculations, buchliite, eithelite, shortite, equation of state, elastic moduli, density of states, pressure.

Optimal Bidding Strategy for Social Welfare Maximization in Wind Farm Integrated Deregulated Power System Using Artificial Gorilla Troops Optimizer Algorithm

PoolCo electricity trading is one of the most capable bidding practices for executing a centralized energy market model. In the PoolCo market model, each seller and buyer submit their bid price and bid quantity to the independent market operator, which they are ready to sell and buy from the market respectively. The market operator regulates the equilibrium market price and volume by considering the acquiesced bid price and bid quantity to settle the market. To maximize the social welfare of market participants, the optimal bidding strategy of a wind farm integrated system is represented as a centralized power market model. Initially, the bid price and bid quantity for consumers and suppliers have been calculated using the Monte-Carlo simulation (MCS) approach. Secondly, a wind farm is incorporated into the system with the help of locational marginal price (LMP). The market operator determines market clearing price (MCP) and market clearing volume (MCV) based on the submitted bid price and bid quantity of suppliers and buyers in order to find the eligible buyers and suppliers. After obtaining MCP and MCV, the market operator reschedules the supplier’s bid quantity with the help of an artificial gorilla troops optimizer (AGTO) algorithm to maximize social welfare by pleasing the system constraints. The AGTO algorithm is used here for the first time to solve the market-clearing power simulation (MCPS) problem with the integration of wind farm. To show the feasibility and effectiveness of the proposed bidding strategy, modified IEEE 14-bus and modified IEEE 30-bus test systems are used here along with a wind farm of 5 MW and 30 MW rated capacity, respectively. Results obtained by using the AGTO algorithm have been compared with those obtained by other optimization algorithms like honey badger algorithm (HBA), artificial bee colony (ABC), particle swarm optimizer (PSO), and slime mould optimizer (SMO) algorithms.

АНАЛІЗ БЕЗЗБИТКОВОСТІ ПІДПРИЄМНИЦЬКОЇ ДІЯЛЬНОСТІ В УМОВАХ ЗМІН

The article deals with the functioning of entrepreneurial activity in the conditions of changes. The peculiarity of entrepreneurial activity is determined, which consists in the correct assessment of the situation and the transformation of difficulties into profit. Economic instability increases the risk and at the same time increases the chances of an entrepreneur who will be able to correctly assess the situation, predict losses and profits. Effective entrepreneurial activity in the face of change depends on the rational use of all types of resources, which necessitates the transition to an optimal cost management system. Methods have been studied that make it possible to quickly assess the impact of the size and structure of costs, the volume of sales of products on profit, analyze its dependence on the price level and production structure, and justify the marketing strategy. The level of break-even production of products or services is analyzed, at which the proceeds from the sale of these products/services (income) are equal to total costs. CVP-analysis is described, which allows optimizing the ratio between variable and fixed costs; optimize the ratio between price and sales volume; minimize business risk; evaluate and predict financial results; identify reserves and ensure an adequate margin of financial stability and justify recommendations for improving activities. The indicators necessary to determine the break-even activity were studied: marginal profit, marginal profit ratio, equilibrium volume of operating activity, level of operational security, and volume of operating activity that provides the target profitability and control lever. CVP analysis should help reduce the risk associated with choosing the right solution. It should be based on accounting information, reporting, plans and forecasts. The break-even analysis of economic activity as a cost management tool has many advantages and, from the point of view of the distribution of fixed costs, provides an objective assessment of performance and enables effective planning, forecasting and cost management. Indeed, in the conditions of change, the problem arises of determining costs, their distribution among objects and ensuring their minimization, management and recognition of expediency, achieving the necessary profitability.

THE INITIAL COMPOSITION AS AN ADDITIONAL PARAMETER DETERMINING THE MELTING BEHAVIOUR OF NANOPARTICLES (A CASE STUDY ON Six-Ge1-x ALLOYS)

Being the basis of modern electronics, silicon-germanium semiconductor alloys are widely used in a great number of fields. In this paper, the phase equilibria in Si-Ge nanoparticles have been simulated using a thermodynamical approach. Calculations show that nanoparticles of different diameters and compositions have unique sets of nanoscale liquidus and solidus temperatures which differ significantly from the reference data for the bulk alloy, and the range between nanoscale liquidus and nanoscale solidus temperatures narrows with reducing the particle size. Unlike bulk alloys, the compositions of co-existing liquid and solid phases at different temperatures dramatically differ in nanoparticles with various Si contents while the dependences of equilibrium phase compositions and volume fractions of co-existing phases on particle diameters have turned out to be different at various temperatures and atomic fractions of Si in a nanoparticle. A thermo-dynamical interpretation of the obtained results has also been given based on several mechanisms of lowering the free energy of the system.

RELATIVE OUTPUT FACTOR (ROF) OF GAMMA KNIFE’S MEASUREMENT USING IONIZATION CHAMBER AND GAFCHROMIC FILMS

<p>The important things on Leksell Gamma Knife (LGK) is determination of Relative Output Factor (ROF), which is required for beam data collection (BDC) process, as an input value to the Treatment Planning System (TPS). The ROF is also needed to traceability of dosimetry measurements and patient safety. ROF measurements on LGK using PTW PinPoint 3D ionization chamber: 0.016 cm<sup>3</sup>, PTW Semiflex: 0.125 cm<sup>3</sup>, and Exradin A16: 0.017 cm<sup>3</sup> at collimators 4, 8 and 16 mm. and gafchromic films. ROF values obtained in hospital-A, using PTW PinPoint 3D was: [(1.00 ± 0.002)], [(0.80 ± 0.02]); [(0.42 ± 0.002)]; and using Exradin A16 [(1.00 ± 0]; [(0, 87 ± 0)]; [(0.69 ± 0.0002)]. And using gafchromic films was: [(1.00 ± 0.006]; (0.96 ± 0.005); (0.86 ± 0.06)]; respectively for collimators 4, 8 and 16 mm, and Measurement of ROF in hospital-B using using a PTW PinPoint 3D was: [(1 ± 0); (0.75 ± 0); and (0.33 ± 0)] and using Exradin A16 was: [(1; 0.87; and 0.69)] and gafchromic films was: [(1.00 ± 0.03); (0.98 ± 0.045); and (0.85 ± 0.09)]; The results of ROF’s measurement were compared with the ROF values of Novotny, et al (2009) and TPS. The Gafchromic’s ROF values were relatively closer than both of them, while the ROF value of ionization. chamber at 4 mm collimators was relatively lower, because measurement in a small field occurs an averaging effect volume and lack of lateral charge particle equilibrium (LCPE).</p>

The superexchange mechanism in crystalline compounds. The case of KMF3 (M = Mn, Fe, Co, Ni) perovskites

The ferromagnetic and antiferromagnetic wavefunctions of four KMF3 (M = Mn, Fe, Co and Ni) perovskites have been obtained quantum-mechanically with the CRYSTAL code, by using the Hartree–Fock (HF) Hamiltonian and three flavours of DFT (PBE, B3LYP and PBE0) and an all-electron Gaussian type basis set. In the Fe and Co cases, with d6 and d7 occupation, the Jahn–Teller distortion of the cubic cell is as large as 0.12 Å. Various features of the superexchange interaction energies (SIE), namely additivity, dependence on the M–M distance, on the angle, and on the adopted functional, are explored. The contribution to SIE by the Coulomb, exchange and kinetic energy terms is analyzed. It is shown that, when using density functionals, SIE clearly correlates with the amount of exact (Hartree–Fock) exchange in the functional. The effect of SIE on the equilibrium geometry and volume of the unit cell is discussed, and it is shown that the key quantity is the spin polarization of the (closed shell) F ions along the M–F–M path. The effect of this magneticpressure is evaluated quantitatively for the first time. The superexchange coupling constant J, evaluated at the HF level and through the Ising model, underestimates the experimental values by about 60%–70%. The more sophisticated Yamaguchi model (that takes into account the contamination of the FM and AFM spin states) does not reduce the discrepancy. The B3LYP hybrid functional overestimates the experiments. These last are bracketed by HF and PBE0. For PBE, the overestimation is huge. Finally, Mulliken population data, charge and spin density maps and density of states are used to illustrate the electronic structure.

Strain-stabilized Al-containing high-entropy sublattice nitrides

The impact of configurational entropy, enthalpy, and strain energy on the phase stability of high-entropy materials has not yet been investigated quantitatively. We used ab-initio calculations to predict the driving force for decomposition of 126 equimolar Al-containing high-entropy sublattice nitrides (HESN), which are all metastable with respect to all corresponding equimolar lower-entropy nitride phases. The entropy stabilization of ≈−0.06 eV/at. at 1073 K is overruled by the 0.10-0.27 eV/at. enthalpy-governed driving force for decomposition. Stabilization is however predicted for 22 compositions due to the −0.01 to - 0.28 eV/at. strain energy contribution caused by large differences in equilibrium volume between the HESN and their decomposition products. The predicted stabilities are consistent with diffraction and tomography data of annealed nitride coatings. Hence, it is evident that only strain enables the stabilization of the here studied Al-containing HESN, while the entropic contribution is overruled by endothermic mixing.

Precipitation behavior of δ phase and its effect on stress rupture properties of selective laser-melted Inconel 718 superalloy

The selective laser-melted (SLM) Inconel 718(IN718) specimens were heat-treated with different solution regimes after the hot isostatic pressing (HIP). The results show that δ phase forms at grain boundary and presents needle-like pattern, and the size and volume fraction of δ phase increase with the increase of holding time and the decrease of solution temperature. The equilibrium volume fraction of needle-like δ phase in SLM-built IN718 is higher than that of short rod-like δ phase in forged-IN718 under the same heat treatment. The SLM-built IN718 specimen without δ phase at grain boundary has the best stress rupture properties, while the specimen with the largest volume fraction of δ phase at grain boundary exhibits the worst stress rupture properties. This is attributed to that the needle-like δ phase at grain boundary promotes the nucleation of void-formed cracks and accelerates the deformation damage. The analysis of the responses to the coordinated deformation capacity of grain orientation and grain size indicates that there exist the heterogeneous deformation and stress/strain concentration at grain boundary. The existence of δ phase influences the coordinated deformation capacity and promotes the stress/strain concentration around grain boundary region. Especially, the needle-like δ phase at grain boundary leads to the more detrimental effect on the rupture life and ductility of SLM-built IN718 alloy on compared with the forged-IN718 alloy.

Multifunctional poly(methacrylate ester)s-based terpolymer cryogels with basic amino groups: Correlation of elasticity and structural properties with composition

Dual-responsive cryogel-structured materials open up a whole new field of bio-applications. Either dimethylaminoethyl methacrylate (DMAEMA) as a carrier of basic amino groups or glycidyl methacrylate (GMA) as a carrier of epoxy rings was introduced into hydroxypropyl methacrylate (HPMA) skeleton. pH/thermo-responsive cationic terpolymer cryogels were successfully prepared by varying the feeding DMAEMA/GMA mol percent ratio from 80/0 to 0/80. The presence of GMA imparts hydrophobic character that reduces swelling and provides additional crosslinks leading to a significant increase in the flexibility. Reducing the polymerization temperature below the freezing point of the solvent resulted in harder and non-brittle cryogels. Up to 48% reduction in hydration was observed for terpolymer cryogels containing 70 mol% DMAEMA upon increasing pH of bathing medium from 2.1 to 8.0. This trend confirmed pH-modulated swelling of amine-containing terpolymer gels, and pH-dependent transition point was found to be 7.7. Oscillating swelling/deswelling in response to pH cycles was studied. The water transport was strongly affected by incorporation of hydrophobic component GMA and protonation of amine functional groups. The swelling mechanism was shifted from anomalous to diffusion controlled with increasing GMA and overall swelling processes followed Schott second order dynamic equation. Lower equilibrium volume swelling at constant temperature was achieved by increasing GMA content of the terpolymers. In low temperature range, while DMAEMA-rich terpolymer gels were swollen, swelling decreased significantly when the gels were enriched in GMA and the temperature was raised above 55 °C. Regardless of salt type and Na+ or K+ hydrated ion radii, a significant difference was observed in salt-sensitive swelling in dilute salt solution (below about 10−3 M), which is controlled by the amount of DMAEMA in terpolymer structure. This study would provide novel ideas for the design of (meth)acrylate ester-based cationic terpolymer cryogels and elucidate the relationship between the gel matrix and their special swelling behavior.

Fundamental volatility and informative trading volume in a rational expectations equilibrium

This paper presents a tractable model of asset price with informative trading volume. Investors condition demands on their rational expectations of both the equilibrium price and trading volume. We suggest a new information role of trading volume, which enables the investors to extract continuous information regarding the liquidation value volatility of the risky asset. The liquidation value volatility determines the relative importance of fundamental value and noise trading in the price function. It also monotonically increases the price volatility. We provide an explanation of the negative and nonlinear relationship between price volatility and trading volume. We also examine the effects of information accuracy and investor composition on the equilibrium price distribution and trading volume.

One-Year Committed Exercise Training Reverses Abnormal Left Ventricular Myocardial Stiffness in Patients With Stage B Heart Failure With Preserved Ejection Fraction.

Individuals with left ventricular (LV) hypertrophy and elevated cardiac biomarkers in middle age are at increased risk for the development of heart failure with preserved ejection fraction. Prolonged exercise training reverses the LV stiffening associated with healthy but sedentary aging; however, whether it can also normalize LV myocardial stiffness in patients at high risk for heart failure with preserved ejection fraction is unknown. In a prospective, randomized controlled trial, we hypothesized that 1-year prolonged exercise training would reduce LV myocardial stiffness in patients with LV hypertrophy. Forty-six patients with LV hypertrophy (LV septum >11 mm) and elevated cardiac biomarkers (N-terminal pro-B-type natriuretic peptide [>40 pg/mL] or high-sensitivity troponin T [>0.6 pg/mL]) were randomly assigned to either 1 year of high-intensity exercise training (n=30) or attention control (n=16). Right-heart catheterization and 3-dimensional echocardiography were performed while preload was manipulated using both lower body negative pressure and rapid saline infusion to define the LV end-diastolic pressure-volume relationship. A constant representing LV myocardial stiffness was calculated from the following: P=S×[Exp {a (V-V0)}-1], where "P" is transmural pressure (pulmonary capillary wedge pressure - right atrial pressure), "S" is the pressure asymptote of the curve, "V" is the LV end-diastolic volume index, "V0" is equilibrium volume, and "a" is the constant that characterizes LV myocardial stiffness. Thirty-one participants (exercise group [n=20]: 54±6 years, 65% male; and controls (n=11): 51±6 years, 55% male) completed the study. One year of exercise training increased max by 21% (baseline 26.0±5.3 to 1 year later 31.3±5.8 mL·min-1·kg-1, P<0.0001, interaction P=0.0004), whereas there was no significant change in max in controls (baseline 24.6±3.4 to 1 year later 24.2±4.1 mL·min-1·kg-1, P=0.986). LV myocardial stiffness was reduced (right and downward shift in the end-diastolic pressure-volume relationship; LV myocardial stiffness: baseline 0.062±0.020 to 1 year later 0.031±0.009), whereas there was no significant change in controls (baseline 0.061±0.033 to 1 year later 0.066±0.031, interaction P=0.001). In patients with LV hypertrophy and elevated cardiac biomarkers (stage B heart failure with preserved ejection fraction), 1 year of exercise training reduced LV myocardial stiffness. Thus, exercise training may provide protection against the future risk of heart failure with preserved ejection fraction in such patients. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03476785.

Structural, electronic and magnetic properties of GdNi5 and its derivatives GdNi3T2 (T = Cr, Fe and Co) alloys

Physical properties of GdNi5, GdNi3Cr2, GdNi3Co2 and GdNi3Fe2 intermetallic compounds have been investigated in the spin-polarized case, using density functional theory. Structural equilibrium parameters of these compounds have been calculated and show that the equilibrium volume (V0) is increasing with the increase of the metal transition atomic radii, also formation energy (Ef) was calculated. The band structure and density of states have been investigated; the results show that the densities of states and band structures of the pure GdNi5 compound are affected by substitution with d metal atoms (Cr, Co and Fe). This influence is observed in the appearance of others peaks in the spectral data. The partial and total magnetic moments of binary GdNi5, and their ternary derivatives GdNi3T2 (T ​= ​Cr, Fe and Co) are also changed in this work by the substitution of Cr, Co and Fe with Ni atom in 2c position site.

Half-metallic, magneto-optic, and thermoelectric properties of CoRuVZ (Z=Al, Ga)

Based on the density functional theory, structural, phonon stability, half-metallic, optical, magneto-optical, and thermoelectric properties of CoRuVAl and CoRuVGa compounds have been calculated. In the ferromagnetic phase, these compounds have equilibrium volumes. Elastic coefficients and their related parameters indicate the elastic stability of these compounds. Moreover, the B/G ratio indicates their ductile behavior. Phonon scattering in the first Brillouin zone in both compounds indicates dynamic stability. The electrical properties of these compounds with GGA+U+mBJ approximation demonstrate half-metallic behavior with a spin-flip gap of 1.5 eV and 1.2 eV for CoRuVAl and CoRuVGa, respectively. Kerr and Epsilon angles of these compounds have significant peaks in the visible region, representing large polarization leading to proper magneto-optical behavior in the visible region. Thermoelectric parameters such as the figure of merit and Seebeck coefficients indicate that these compounds are suitable for thermoelectric applications at room temperature.

Competition between Osmotic Squeezing versus Friction-Driven Swelling of Gels.

Some types of hydro-gels have almost the same equilibrium swelling volume in water and in ethylene glycol (EG), a highly viscous liquid completely miscible with water. Experiments showed that when a gel fully swollen with EG is immersed into a large amount of water, it temporarily swells up and then relaxes to the equilibrium volume in water. The temporary swelling is explained by the friction force exerted on the gel network from the outward EG flux In this paper, we experimentally show that the temporary swelling is suppressed by adding linear PEG (polyethylene glycol) in the outer water. Although the suppression seems to be explained by the osmotic pressure (i.e., by the same mechanism as the conventional osmotic squeezing), our theoretical analysis reveals that the effect of PEG is much stronger than that expected from the equilibrium osmotic pressure, implying that the PEG chains are condensed on the gel surface.

Temperature-dependent elastic properties of high entropy ceramic (ZrTaNbTi)C from self-consistent quasi-harmonic approximation

High-entropy ceramics have recently attracted considerable attentions because of excellent combination of exceptional properties. In this work, the temperature dependent elastic properties of (ZrTaNbTi)C have been systematically studied from the density functional perturbation theory combined with self-consistent quasi-harmonic approximation. High entropy ceramic (ZrTaNbTi)C is thermodynamically stable due to the negative formation enthalpy, and is also mechanically stable from the obtained elastic properties. The phonon dispersion relation computed at equilibrium volume contains no imaginary-frequency, implying the dynamical stability. At 0 K, (ZrTaNbTi)C possesses evidently high elastic moduli and hardness. The calculated electronic density of state and Bader charge at 0 K and 2000 K show that (ZrTaNbTi)C have covalent characteristics accompanied by ionic feature while the covalency decreases and the ionicity increases as temperature increases. The temperature-dependent elastic properties show that (ZrTaNbTi)C is mechanically stable in temperature range studied, and remains high strength and hardness at high temperature due to the slight softening of strong covalent bonding. Poisson's ratio, Pugh's ratio and Cauchy pressure suggest the higher brittle-ductile transformation trend as the temperature increases. Moreover, (ZrTaNbTi)C shows less anisotropy at higher temperature from the Zener index AZ and three-dimensional projections, being beneficial to reduce cracking and improve durability. The present study provides more insight into the high temperature behavior of mechanical properties, would be valuable for understanding and design of high-temperature properties of high entropy carbide ceramics.

In Situ Pseudopotentials for Electronic Structure Theory.

We present a general method of constructing in situ pseodopotentials from first-principles, all-electron, and full-potential electronic structure calculations of a solid. The method is applied to bcc Na, at low-temperature equilibrium volume. The essential steps of the method involve (i) calculating an all-electron Kohn–Sham eigenstate, (ii) replacing the oscillating part of the wave function (inside the muffin-tin spheres) of this state, with a smooth function, (iii) representing the smooth wave function in a Fourier series, and (iv) inverting the Kohn–Sham equation, to extract the pseudopotential that produces the state generated in steps i–iii. It is shown that an in situ pseudopotential can reproduce an all-electron full-potential eigenvalue up to the sixth significant digit. A comparison of the all-electron theory, in situ pseudopotential theory, and the standard nonlocal pseudopotential theory demonstrates good agreement, e.g., in the energy dispersion of the 3s band state of bcc Na.

Molecular dynamics study of the point defects in bcc uranium

Thermodynamic properties of bcc uranium with point defects are studied using ab initio molecular dynamics (MD) simulations at 1100 K. The simulations were performed with canonical ensembles of ${\mathrm{U}}_{127}{\mathrm{M}}_{1}$, ${\mathrm{U}}_{128}{\mathrm{M}}_{1}$, and ${\mathrm{U}}_{126}{\mathrm{M}}_{1}{\ensuremath{\square}}_{1}$ for M = $\ensuremath{\square}$, He, Ne, Ar, Kr, Xe, Sr, Zr, I, Cs, and Pu disposed on a bcc lattice lying within a $4\ifmmode\times\else\texttimes\fi{}4\ifmmode\times\else\texttimes\fi{}4$ cubic supercell. This work provides formation energies of substitutional, self, and solute interstitial atom defects as well as binding energies of M-$\ensuremath{\square}$ pair defects. This work demonstrates that our computational scheme based on MD simulations gives reliable formation and binding energies of atomic defects in bcc uranium compared to conventional density functional theory calculations. The equilibrium volume, bulk modulus, and thermal expansion coefficient of pure bcc uranium obtained from our MD simulations compare very well with corresponding experimental results. The vacancy formation energy is predicted to be 0.88 eV. The experimental vacancy formation energy remains uncertain. Experimental study of the formation and binding energies of other point defects as well as the bulk modulus and thermal expansion coefficients of uranium with these defects is also not found in the literature. This work shows that point defects tend to decrease the bulk modulus and increase the thermal expansion coefficient of bcc uranium. The solute formation energies of noble gas atoms show a bearing on their size. A large solute (Xe) has a high formation energy, and vice versa. This size effect is not quite evident for the chemically reactive solutes, namely, Sr, Zr, I, Cs, and Pu. Our MD simulations further show that vacancies are the favorable point defects in bcc uranium rather than both vacancies and self interstitials as predicted by earlier calculations. The formation energies of self interstitial atoms are found to be lower than those of solute interstitial atoms, each calculated in six different basic interstitial dumbbell configurations. That is, bcc U accommodates self interstitials more easily than decay or fission gas interstitials (He, Kr, and Xe). Further, He atoms are found to have comparable formation energies in the substitutional and interstitial locations. The fission product atoms Kr and Xe prefer to occupy vacant substitutional lattice sites rather than interstitial sites. Binding energies of divacancy and solute-vacancy pairs (0.31 vs $\ensuremath{-}0.69$ eV for the Xe-$\ensuremath{\square}$ pair, for instance) from our MD simulation show that nucleation and growth of fission gas bubbles are supported by a thermodynamic driving force, whereas vacancies tend to stay apart. This is in agreement with literature reporting that bcc uranium softens and swells mainly by agglomeration of noble gas bubbles.

Assessment of radiation hazard of uranium enterprises for the environment

The purpose of the article is to describe monitoring studies on the radiation state of air in populated and working areas near the uranium processing enterprise in the Republic of Uzbekistan. Ac-cording to the analytical measurement, the exposure dose of gamma radiation is equivalent to the equilibrium volume activity of radon, specific activity of long-lived alpha-emitting nuclides in the zone of influence of the enterprise, the working area, premises for storing uranium materials and manufacturing dumps, tailings dams and areas of underground uranium leaching. It was shown that the measurement results do not exceed the regional background and regulatory levels of radioactive radiation by all indicators. The dependence of the volume activity of radon at production facilities on the density of the radon flux from the soil was studied. The most intensive radioactive objects – uranium dumps – were identified. It was found out that there is no excess radioactive impact of the uranium enterprise on the environmental objects.