Influence of Antiferromagnetic Fluctuations on the Fulde–Ferrell–Larkin–Ovchinnikov State in CeCoIn5

The Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state is a spatially inhomogeneous superconducting (SC) phase with a periodically modulated order parameter predicted to appear in sufficiently clean type-II superconductors, close to the upper critical field, if the orbital pair breaking is small relative to the Pauli-limiting effect. The heavy-fermion superconductor CeCoIn₅ is the first material, where different physical probes show strong experimental evidence pointing to the realization of the FFLO state, even though strong antiferromagnetic (AFM) spin-fluctuations (SF) are present at atmospheric pressure. To study the influence of the AFM-SF on the FFLO state we performed heat-capacity experiments under pressure. We utilized a newly developed miniature piston-cylinder type pressure cell specially suited for measuring small samples at high-magnetic fields and low temperatures (0 GPa ≤ P ≤ 1.5 GPa, 0 kOe ≤ H ≤ 140 kOe, and 100 mK ≤ T ≤ 4 K). We found the second anomaly inside the SC state in CeCoIn5 can still be observed with pressure, which suppress the strong AFM-SF. The FFLO phase extends to higher fields and temperatures on applying pressure while the Pauli-limiting effect is becoming weaker and the SF are suppressed. This reveals the detrimental effect of the AFM-SF on the FFLO phase stability.      

Method of the shortcut estimation of rails' reliability by the fatigue strength criterion

The diagram of damage of structural steels under bending and contact loading has been constructed. The criterion of the critical state of steels is proposed, which corresponds to the formation of incipient surface cracks in the rolling friction zone. The methods of shortcut estimation of the damaged state of railway rails, which provide prediction of their reliability and life under service conditions, are proposed. A set of experimental studies is made with objectives to justify the proposed diagram, criterion and methods. __________ Translated from Problemy Prochnosti, No. 1, pp. 88–94, January–February, 2009.     

On the static equilibrium of an elastic orthotropic medium with an arbitrarily oriented elliptical crack

We analyze the problem of the stress distribution in an elastic orthotropic medium with an arbitrarily oriented elliptical crack. To construct the problem solution, the Willis approach is used which is based on the triple Fourier transformation of spatial variables and Fourier-image of Green’s function for an infinite anisotropic space. The investigation results in special cases are compared with the data of other authors. The effect of the elliptical crack orientation in an orthotropic space on the distribution of the stress intensity factors along its contour is studied. __________ Translated from Problemy Prochnosti, No. 4, pp. 146–159, July–August, 2007.     

On the analysis of stress state in elliptical tensile neck

The tensile necking in cylindrical and plate specimens is described based on a modification of the Bridgman theory for an isotropic case. A method of determination of principal stress trajectories in an elliptical tensile neck is put forward, which involves transformation of the initial coordinate grid by means of conformal mappings. Expressions are derived for the principal stresses and the radius of curvature of stress trajectories. Based on assumptions that depart from the Bridgman theory, an approximate analytical solution is obtained for the stress distribution in specimens with an elliptical cross-section. The new solution belongs to the one-parameter family of solutions which includes the Bridgman’s and Davidenkov–Spiridonova’s solutions. Translated from Problemy Prochnosti, No. 4, pp. 19–28, July–August, 2009.     

Effect of the layout of small-and large-series WWER-1000 reactors of nuclear power plants on the stress-strain state of the header-steam generator connector weldment

Refined results of the stress-strain state evaluation for the hot header-steam generator connector weldment of small-and large-series WWER-1000 reactors with three-dimensional models are presented. The layout of the steam generators in the reactors is shown to influence maximum stresses in the vicinity of the weld. __________ Translated from Problemy Prochnosti, No. 5, pp. 114–120, September–October, 2007.     

Study of Superconducting State Parameters of Binary Metallic Glasses by Pseudopotential Method

The theoretical calculation of the superconducting state properties (SSP) viz electron–phonon coupling strength λ, Coulomb pseudopotential μ ^*, transition temperature T _C , isotope effect exponent α and effective interaction strength N _O V of 50 binary metallic glasses of simple, non-simple, and transition metals have been carried out using a well-recognized model potential. We have employed here five different types of local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru–Utsumi (IU), Farid et al. (F), and Sarkar et al. (S) to study the exchange and correlation effects on the present investigations. Instead of using Vegard’s law, a pseudo-alloy-atom model (PAA) in the present investigation is proposed and found successful. The present results of the SSP are found to be in qualitative agreement with other such earlier reported data wherever they exist, which confirms the superconducting phase in the metallic glasses.     

Influence of the mechanism and parameters of hardening of modified novolac phenol-formaldehyde resins on the physicomechanical properties of the composite

We study the influence of concentrations of the components of reactive compositions and the conditions of production and hardening of phenol-formaldehyde resins with the help of epoxy resins in the presence of polyvinylpyrrolidone on the physicomechanical, thermal, adhesion, insulation, and anticorrosion properties of the composites. The positive effect of modifications with polyvinylpyrrolidone and epoxy resin manifests itself within the following ranges of concentrations: 0.5–1 wt.% of polyvinylpyrrolidone and 25–30 wt.% of ED-20 in the presence of 1 wt.% of N, N-dimethylaniline. Thus, the adhesion strength of a glue based on the developed composition becomes four times higher and constitutes 5–6 MPa; the impact strength, static strength in bending, surface hardness, and the specific bulk electric resistance of the specimens hardened at 150–160°C for 25–30 min become 1.5–2.5 times higher and are equal to 5–6J/m², 15–17 MPa, 350–420 MPa, and (5.5–6.5)⋅10¹⁰ Ω⋅m, respectively. The behavior of these characteristics strongly depends on the conditions of hardening. We optimized the composition of modified phenol-formaldehyde resins, which made it possible to produce materials with predicted properties.     

Deformation-driven formation of equilibrium phases in the Cu–Ni alloys

The homogeneous coarse-grained (CG) Cu–Ni alloys with nickel concentrations of 9, 26, 42, and 77 wt% were produced from as-cast ingots by homogenization at 850 °C followed by quenching. The subsequent high-pressure torsion (5 torsions at 5 GPa) leads to the grain refinement (grain size about 100 nm) and to the decomposition of the supersaturated solid solution in the alloys containing 42 and 77 wt% Ni. The lattice spacing of the fine Cu-rich regions in the Cu–77 wt% Ni alloy was measured by the X-ray diffraction (XRD). They contain 28 ± 5 wt% Ni. The amount of the fine Ni-rich ferromagnetic regions in the paramagnetic Cu–42 wt% Ni alloy was estimated by comparing its magnetization with that of fully ferromagnetic Cu–77 wt% Ni alloy. According to the lever rule, these Ni-rich ferromagnetic regions contain about 88 wt% Ni. It means that the high-pressure torsion of the supersaturated Cu–Ni solid solutions produces phases which correspond to the equilibrium solubility limit at 200 ± 40 °C (Cu–77 wt% Ni alloy) and 270 ± 20 °C (Cu–42 wt% Ni alloy). To explain this phenomenon, the concept of the effective temperature proposed by Martin (Phys Rev B 30:1424, 1984) for the irradiation-driven decomposition of supersaturated solid solutions was employed. It follows from this concept that the deformation-driven decomposition of supersaturated Cu–Ni solid solutions proceeds at the mean effective temperature T _eff = 235 ± 30 °C. The elevated effective temperature for the high-pressure torsion-driven decomposition of a supersaturated solid solution has been observed for the first time. Previously, only the T _eff equal to the room temperature was observed in the Al–Zn alloys.     

Life estimation for high-strength materials under cyclic loading in the multiaxial stress state

The life of high-strength materials under cyclic loading in the multiaxial stress state is experimentally estimated using the deformation-kinetic criterion. Translated from Problemy Prochnosti, No. 2, pp. 139–143, March–April, 2009.     

Generalized relative characteristics of limiting states of material under nonisothermal deformation

We describe a procedure for representing material characteristics as thermodynamic invariants. It has enabled us to put forward arguments of equations for limiting mechanical states under nonisothermal deformation for similar materials. The procedure is based on relations of a simple theory of fracture and on the concepts of the similarity theory and dimensional analysis theory. Translated from Problemy Prochnosti, No. 3, pp. 45–57, May–June, 2009.     

Indirect measurement of state variables for the diagnostics of electromechanical systems

A method of estimating the actual state of electromechanical systems based on the use of a model, connected in parallel with the diagnosed equipment, and an indirect measurement of the state variables is considered. A diagnostic system structure is proposed and also versions of models which take the operating features into account. __________ Translated from Izmeritel’naya Tekhnika, No. 7, pp. 43–46, July, 2007.     

Effect of polymers on the nanostructure and on the carbonation of calcium silicate hydrates: a scanning transmission X-ray microscopy study

This study investigated the effects of organic polymers (polyethylene glycol and hexadecyltrimethylammonium) on structures of calcium silicate hydrates (C–S–H) which is the major product of Portland cement hydration. Increased surface areas and expansion of layers were observed for all organic polymer modified C–S–H. The results from attenuated total reflectance–Fourier transform infrared (ATR–FTIR) spectroscopic measurements also suggest lowered water contents in the layered structures for the C–S–H samples that are modified by organic polymers. Scanning transmission X-ray microscopy (STXM) results further supports this observation. We also observed difference in the extent of C–S–H carbonation due to the presence of organic polymers. No calcite formed in the presence of HDTMA whereas formation of calcite was observed with C–S–H sample modified with PEG. We suggest that the difference in the carbonation reaction is possibly due to the ease of penetration and diffusion of the CO₂. This observation suggests that CO₂ reaction strongly depends on the presence of organic polymers and the types of organic polymers incorporated within the C–S–H structure. This is the first comprehensive study using STXM to quantitatively characterize the level of heterogeneity in cementitious materials at high spatial and spectral resolutions. The results from BET, XRD, ATR–FTIR, and STXM measurements are consistent and suggest that C–S–H layer structures are significantly modified due to the presence of organic polymers, and that the chemical composition and structural differences among the organic polymers determine the extent of the changes in the C–S–H nanostructures as well as the extent of carbonation reaction.     

Kinetic Theory of Creep and Creep-Rupture Strength Analysis of Structural Components. Part 2. Limiting State of Non-Uniformly Heated Structural Components

For an arbitrary body (a structural member) subjected to external steady temperature and force actions, a limiting state condition which ensures the uniform strength of the body until its load-carrying capacity is exhausted has been derived using Rabotnov's kinetic theory of creep. A procedure of strength analysis of structural members by the limiting state is put forward. For the case where the limiting state condition is fulfilled only on some individual portions of the body's surface, a procedure of calculating its stress-strain state with the nearest approach to the uniform-strength state is outlined. __________ Translated from Problemy Prochnosti, No. 6, pp. 5 – 14, November – December, 2005.     

Determination of the temperature corrections to the readings of measuring instruments under dynamic temperature conditions

A method of obtaining the temperature corrections to readings of measuring instruments, taking their thermal inertia into account, when the temperature of the medium changes is proposed. The procedure was tested under laboratory conditions on static nonthermostated gravimeters. The results of the investigations, which confirm the effectiveness of the proposed procedure, are presented. __________ Translated from Izmeritel’naya Tekhnika, No. 1, pp. 50–52, January, 2007.     

Liquid Saturation Density from Simple Equations of State

Several simple equations of state, requiring only two input properties, have been studied in order to determine the liquid saturation density of 144 fluids of different kinds. This study includes old and new simple modifications of the van der Waals equation of state, and the Carnahan–Starling–Yelash–Kraska and Carnahan–Starling–Dieterici equations. The new simple modifications of the van der Waals equation give better overall results than some other more complex proposed equations, especially near the critical point. The recent equation proposed by Eslami including the boiling temperature and density as input parameters was also checked, and was found not to reproduce the critical point, but to give excellent results at intermediate or low temperatures. As a reference, the behavior of the well-known Soave– Redlich–Kwong and Peng–Robinson equations, and the more recent expression proposed by Mohsen-Nia et al. that requires three input parameters were also checked. The latter does not improve the accuracy of the Peng–Robinson equation, and very simple van-der-Waals type equations give better overall results.     

Kinetic Theory of Creep and Creep-Rupture Strength Analysis of Structural Components. Part 1. Stress-Strain State in Nonuniformly Heated Thick-Walled Pipes

The stress-strain state and the failure onset time are calculated by Rabotnov's kinetic theory of creep for a thick-walled nonuniformly heated pipe loaded by internal pressure. We analyze the influence of the temperature difference along the pipe radius on the stress intensity distribution and damageability parameter of material in the pipe cross section at various instants of time up to the rupture onset. Based on the comparative analysis, we proved incompatibility of the results obtained by the above-mentioned theory with those calculated by the similar theory of creep in the Kachanov's statement. __________ Translated from Problemy Prochnosti, No. 5, pp. 30 – 44, September – October, 2005.     

A method for fracture toughness assessment by the scatter of hardness characteristics

A stable correlation between the material fracture toughness characteristics and statistical parameters of scatter of hardness values has been established. __________ Translated from Problemy Prochnosti, No. 6, pp. 5–12, November–December, 2007.     

Correlation for the Carbon Dioxide and Water Mixture Based on The Lemmon–Jacobsen Mixture Model and the Peng–Robinson Equation of State

Models representing the thermodynamic behavior of the CO₂–H₂O mixture have been developed. The single-phase model is based upon the thermodynamic property mixture model proposed by Lemmon and Jacobsen. The model represents the single-phase vapor states over the temperature range of 323–1074 K, up to a pressure of 100 MPa over the entire composition range. The experimental data used to develop these formulations include pressure–density–temperature-composition, second virial coefficients, and excess enthalpy. A nonlinear regression algorithm was used to determine the various adjustable parameters of the model. The model can be used to compute density values of the mixture to within ±0.1%. Due to a lack of single-phase liquid data for the mixture, the Peng–Robinson equation of state (PREOS) was used to predict the vapor–liquid equilibrium (VLE) properties of the mixture. Comparisons of values computed from the Peng–Robinson VLE predictions using standard binary interaction parameters to experimental data are presented to verify the accuracy of this calculation. The VLE calculation is shown to be accurate to within ±3 K in temperature over a temperature range of 323–624 K up to 20 MPa. The accuracy from 20 to 100 MPa is ±3 K up to ±30 K in temperature, being worse for higher pressures. Bubble-point mole fractions can be determined within ±0.05 for CO₂.