The parameters governing the coefficient of dispersion of cubes in rotating cylinders

Axial dispersion of cubic particles in horizontal, rotating cylinders was investigated using discrete element modelling simulations. We found that, similar to the behavior of spheres, the axial dispersion coefficient of cubes depends on (1) the rotational speed of the cylinder \({\omega }\), (2) the acceleration due to gravity g and (3) the particle size d, satisfying the relationship \({D}_\mathrm {ax}\propto {\omega }^{1-2{\lambda }}{g}^{{\lambda }}{d}^{2-{\lambda }}\) with \({\lambda }\approx 0.15\) (\({\lambda }\approx 0.1\) for beds of spheres) (Third et al. in Powder Technol 203:510–517, 2010). This observation suggested that, although particle shape influences significantly the rate of axial dispersion (cubes disperse almost twice as fast as spheres of equal volume), the parameters controlling the coefficient of dispersion are independent of particle shape.     

Physical,optical and structural studies of copper-doped lead oxychloro borate glasses

Bluish coloured glasses are obtained from the composition PbCl\(_{2}\)–PbO–B\(_{2}\)O\(_{3}\) doped with Cu\(^{2+}\) ions. Basic physical properties and spectroscopic studies (optical absorption, electron paramagnetic resonance, Fourier transform infrared and Raman spectroscopies) were carried out on these samples. The increase in PbCl\(_{2}\) content resulted in the decrease in density and increase in molar volume. At optical frequencies, band gaps and Urbach energies were evaluated and their variation is explained. Spin-Hamiltonian parameters (SHP) obtained from the EPR spectra suggest that the ligand environment around Cu\(^{2+}\) is tetragonally distorted octahedral sites and the orbital \(d_{x^{2}-{y}^{2}} \) is the ground state. The characteristics broad bands in the optical absorption spectra are assigned to the \(^{2}\)B\(_{\mathrm{1g}}\,\rightarrow \, {}^{2}\)B\(_{\mathrm{2g}}\) transition. The bonding coefficient values were evaluated using optical data and SHP. FTIR studies suggested that the glass structure is built up of BO\(_{3}\) and BO\(_{4}\) units. The presence of diborate, pyroborate, pentaborate groups, etc. in the glass network was confirmed from Raman spectra.     

Effective Thermal-Conductivity Measurement on Germanate Glass–Ceramics Employing the 3\omega Method at High Temperature

It can be noted that the germanate glass–ceramic is a functional material with excellent thermal stability which can be used in optical devices. The temperature-dependent effective thermal conductivities of CaO–BaO–CoO–Al \(_{2}\) O \(_{3}\) –SiO \(_{2}\) –GeO \(_{2}\) glass–ceramics from 295.5 K to 780 K are determined using a \(3\omega \) method. One of the main advantages for the \(3\omega \) method is to diminish radiation errors effectively when the temperature is as high as 1000 K. Thermal conductivities of CaO–BaO–CoO–Al \(_{2}\) O \(_{3}\) –SiO \(_{2}\) –GeO \(_{2}\) increase with a rise in temperature. Effective thermal conductivities of a sample increase from \(1.55~\hbox {W}\cdot \hbox {m}^{-1}\cdot \hbox {K}^{-1}\) at 295.5 K to \(7.64~\hbox {W}\cdot \,\hbox {m}^{-1}\cdot \hbox {K}^{-1}\) at 698.1 K. The effective thermal conductivity of CaO–BaO–CoO–Al \(_{2}\) O \(_{3}\) –SiO \(_{2}\) –GeO \(_{2}\) glass–ceramic increases with a rise of temperature. This investigation can be used as a basis for the measurement of thermal properties of ceramic materials at higher temperature.     

Measurement and Modeling of Mean Activity Coefficients of NaCl in an Aqueous Mixed Electrolyte Solution Containing Glycine

An electrochemical cell with two ion-selective electrodes (Na\(^{+}\) glass) and (Cl\(^{-}\) solid state) was used to measure the mean ionic activity coefficient of NaCl in an aqueous mixture containing NaCl, glycine, and NaNO\(_{3}\) at 308.15 K. The experiments were conducted at fixed molality of NaNO\(_{3}\) (0.1 m) and various molalities of glycine (0–1 m) and NaCl (up to 0.8 m). The experimental data were modeled using a modified version of the Pitzer equation. Finally the activity coefficient ratio of glycine was determined based on the Maxwell equation.     

New aspects for friction coefficients of finite granular avalanche down a flat narrow reservoir

This work examines the bulk internal friction coefficient, \(\mu \), and effective wall friction coefficient, \(\mu _w\), for finite number of nearly identical dry glass spheres in avalanche down a narrow inclined reservoir of smooth frictional bed using a validated discrete element scheme. Instantaneous deviatoric strain rate tensor \(\dot{\gamma }^d_{ij}\) and stress tensor \(\tau _{ij}\) are computed locally to evaluate a three-dimensional constitutive model developed based on the rheology of steady homogeneous surface flows. On one side, the algebraic \(\mu -I\) relation conforms to conventional relation for glass beads, \(\mu =0.34+0.31/(1+0.15/I)\) (Jop et al. in J. Fluid Mech. 541:167–192, 2005, Midi in Eur. Phys. J. E 14:341–365, 2004, Jop in Comptes Rendus Phys. 16:62–72, 2015), when the inertial number \(I>I_{c}=2\times 10^{-2}\). The assumption of collinear \(\tau _{ij}\) and \(\dot{\gamma }^d_{ij}\), however, does not hold and such misalignment agrees to the findings in non-uniform inhomogeneous flows (Cortet et al. in Europhys. Lett. 88(1):14001, 2009). Below \(I_c\), we observe a decaying \(\mu -I\) as found in slowly deforming rheology tests and a simplified model is developed in view of shear-induced dilatation upon yielding. Non-constant effective wall friction coefficient is measured to grow in time and with I towards the sphere-wall sliding friction coefficient in the contact model while preserving the depth-weakening feature as in confined steady surface flows (Richard et al. in Phys. Rev. Lett. 101:248002, 2008, Brodu et al. in Phys. Rev. E 87:022202, 2013). The fact that rotation at one sphere center can divert surface relative velocity across the contact area to render lower sliding friction is considered to develop a model describing how \(\mu _w\) drops with the ratio between rotation-induced velocity and sliding velocity, \(\varOmega \). The simulation data compares fairly well to the predicted monotonic decay of \(\mu _w\) with \(\varOmega \).     

Investigating mechanism of inclined CPT in granular ground using DEM

This paper presents an investigation on mechanism of the inclined cone penetration test using the numerical discrete element method (DEM). A series of penetration tests with the penetrometer inclined at different angles (i.e., \(0^{\circ },\,15^{\circ },\,30^{\circ },\,45^{\circ }\) and \(60^{\circ }\) ) were numerically performed under \(\mu =0.0\) and \(\mu =0.5\) , where \(\mu \) is the frictional coefficient between the penetrometer and the soil. The deformation patterns, displacements of soil particles adjacent to the cone tip, velocity fields, rotations of the principal stresses and the averaged pure rotation rate were analyzed. Special focus was placed on the effect of friction. The DEM results showed that soils around the cone tip experienced complex displacement paths at different positions as the inclined penetration proceeded, and the friction only had significant effects on the soils adjacent to the penetrometer side and tip. Soils exhibited characteristic velocity fields corresponding to three different failure mechanisms and the right side was easier to be disturbed by friction. Friction started to play its role when the tip approached the observation points, while it had little influence on rotation rate. The normalized tip resistance \((q_{c}=f/\sigma _{v0})\) increased with friction as well as inclination angle. The relationship between \(q_{c}\) and relative depth \((y/R)\) can be described as \(q_{c}=a\times (y/R)^{-b}\) , with parameters \(a\) and \(b\) dependent on penetration direction. The normalized resistance perpendicular to the penetrometer axis \(q_{p}\) increases with the inclination angle, thus the inclination angle should be carefully selected to ensure the penetrometer not to deviate from its original direction or even be broken in real tests.     

Structural and physical properties of $$\hbox {Sm}^{3+}$$ doped magnesium zinc sulfophosphate glass

Samarium (\(\hbox {Sm}^{3+})\) doped magnesium zinc sulfophosphate glass system of composition (60–\(x)\hbox {P}_{2}\hbox {O}_{5}\)–20MgO–20ZnSO\(_{4}\)–\(x\hbox {Sm}_{2}\hbox {O}_{3}\) (\(x =\) 0.0, 0.5, 1.0, 1.5 and 2.0 mol%) were synthesized using melt-quenching technique. The structure and physical properties of prepared glass samples were characterized. The X-ray diffraction pattern verified their amorphous nature. The physical properties such as density, refractive index, molar volume, rare earth ion concentration, etc. were calculated. The decrease in the optical bandgap energy with increasing \(\hbox {Sm}_{2}\hbox {O}_{3}\) contents was attributed to the alteration in the glass network structures. Fourier transformed infrared spectra and Raman analyses manifested the depolymerization of \(\hbox {ZnSO}_{4}\) in the phosphate host matrix. The present findings may be beneficial for the advancement of functional glasses.     

Stress Assessment in Precipitation Hardened IN718 Nickel-Base Superalloy Based on Hall Coefficient Measurements

The feasibility of residual stress assessment in precipitation hardened IN718 nickel-base superalloy based on Hall coefficient measurement is investigated through studying the influence of thermal hardening, cold work, and applied stress. Measurements in IN718 specimens of various hardness levels show that the Hall coefficient increases from 8 ± 0.1\(\,\times \,\)10\(^{-11}\) m\(^{3}\)/C in the fully annealed state of 14 HRC to 9.4 ± 0.1\(\,\times \,\)10\(^{-11}\) m\(^{3}\)/C in the fully hardened state of 45 HRC. Measurements in IN718 specimens of various cold work levels show that plastic deformation exerts negligible effect on the Hall coefficient of fully annealed IN718, while in fully hardened IN718 the Hall coefficient decreases more or less linearly with cold work from its peak value of 9.4 ± 0.1\(\,\times \,\)10\(^{-11}\) m\(^{3}\)/C in its intact state to 8.9 ± 0.1\(\,\times \,\)10\(^{-11}\) m\(^{3}\)/C in its most deformed state of 22% plastic strain. Measurements taken under applied stress show that elastic strain significantly increases the Hall coefficient of IN718 regardless of the state of hardening. The relative sensitivity of the Hall coefficient to elastic strain is called the galvanomagnetic gauge factor and defined as the ratio of the relative change of the Hall coefficient divided by the axial strain under applied uniaxial stress. The gauge factor of IN718 is in the range of 2.6–2.9 depending on the hardness level. Besides the fairly high value of the gauge factor, it is important that it is positive, which means that compressive stress in surface-treated components decreases the Hall coefficient in a similar way as plastic deformation does, therefore the unfortunate cancellation that occurs in fully hardened IN718 in the case of electric conductivity measurements does not happen in this case. In addition, the influence of thermal exposure up to 700 \({{}^{\circ }}\)C and the reversible temperature dependence of the Hall coefficient at room temperature are studied in IN718 at different hardness levels.     

First-Principles Investigations on Structural,Phonon, and Thermodynamic Properties of Cubic \text {CeO}_{2}

The structural, phonon, and thermodynamic properties of the cubic \(\hbox {CeO}_{2}\) are investigated from first-principles calculations. The calculated lattice parameters, bulk modulus, and phonon dispersion curves are in agreement with available experimental data and other calculations. It is shown that the local density approximation (LDA)+ \(U\) method is more suitable for describing the properties of \(\hbox {CeO}_{2}\) compared with the LDA method. The pressure and temperature dependences of the specific heat, Debye temperature, and the thermal expansion coefficient are successfully obtained from the Debye–Grüneisen model by combining with the phonon density of states.     

In situ synthesis and properties of self-reinforced $$\hbox {Si}_{3} \hbox {N}_{4}\textendash \hbox {SiO}_{2}\textendash \hbox {Al}_{2} \hbox {O}_{3}\textendash \hbox {Y}_{2}\hbox {O}_{3} \ (\hbox {La}_{2}\hbox {O}_{3}$$) glass–ceramic composites

In-situ-grown \(\upbeta \!\hbox {-Si}_{3}\hbox {N}_{4}\)-reinforced \(\hbox {SiO}_{2}\textendash \hbox {Al}_{2}\hbox {O}_{3}\textendash \hbox {Y}_{2}\hbox {O}_{3}\) \((\hbox {La}_{2}\hbox {O}_{3})\) self-reinforced glass–ceramic composites were obtained without any \(\upbeta \!\hbox {-Si}_{3}\hbox {N}_{4}\) seed crystal. These composites with different compositions were prepared in a nitrogen atmosphere for comparison of phase transformation and mechanical properties. The results showed that \(\hbox {SiO}_{2}\textendash \hbox {Al}_{2}\hbox {O}_{3}\textendash \hbox {Y}_{2}\hbox {O}_{3}\) \((\hbox {La}_{2}\hbox {O}_{3})\) glass can effectively promote \(\upalpha \)- to \(\upbeta \!\hbox {-Si}_{3}\hbox {N}_{4}\) phase transformation. The crystallized \(\hbox {Y}_{2}\hbox {Si}_{2}\hbox {O}_{7}\textendash \hbox {La}_{4.67}\hbox {Si}_{3}\hbox {O}_{13}\) phases with a high melting point significantly benefited the high-temperature mechanical properties of the composites. The \(\hbox {Si}_{3}\hbox {N}_{4}\textendash \hbox {SiO}_{2}\textendash \hbox {Al}_{2} \hbox {O}_{3}\textendash \hbox {Y}_{2}\hbox {O}_{3}\) \((\hbox {La}_{2}\hbox {O}_{3})\) glass–ceramic composites exhibit excellent mechanical properties compared with unreinforced glass–ceramic matrix, which is undoubtedly attributed to the elongated \(\upbeta \!\hbox {-Si}_{3}\hbox {N}_{4}\) grains. These glass–ceramic \(\hbox {Si}_{3}\hbox {N}_{4}\) composites with excellent comprehensive properties might be a promising material for high-temperature applications.     

Low-Temperature Drift in MIMS Base-Metal Thermocouples

Inhomogeneities are known to develop within thermoelements exposed to elevated temperatures, resulting in temperature measurement errors. While the Seebeck coefficient drift in base-metal thermocouples due to aging at temperatures over \(200\,^{\circ }\mathrm{C}\) has been extensively investigated, there have been very few investigations into possible Seebeck changes at lower temperatures. Despite warnings about possible effects, most practitioners assume changes in homogeneity are either not significant or not able to develop at temperatures less than \(200\,^{\circ }\mathrm{C}\) . This study reports on measurements of inhomogeneities in base-metal thermocouples arising from heat treatment at temperatures in the region of \(200\,^{\circ }\mathrm{C}\) . Thermoelectric scans of thermocouples were carried out following exposure of a range of mineral-insulated metal-sheathed base-metal thermocouples, from two large manufacturers, of Types E, J, K, N, and T, to either a linear-gradient furnace within the range of \(100\,^{\circ }\mathrm{C}\) to \(320\,^{\circ }\mathrm{C}\) or uniform temperature zones of \(100\,^{\circ }\mathrm{C}\) , \(150\,^{\circ }\mathrm{C}\) , and \(200\,^{\circ }\mathrm{C}\) . The experiments reveal noticeable drift in all base-metal types for temperatures as low as \(100\,^{\circ }\mathrm{C}\) and exposure times as short as 1 h. The most sensitive thermoelement alloys appear to be Constantan, Alumel, and Nicrosil. It is concluded that the common working assumption that base-metal thermocouples suffer no thermally induced changes in the Seebeck coefficient below \(200\,^{\circ }\mathrm{C}\) is false. This observation has significant implications for many high-stability monitoring and control systems reliant on base-metal thermocouples that operate in the range of \(100\,^{\circ }\mathrm{C}\) to \(200\,^{\circ }\mathrm{C}\) . Additionally, thermoelectric scanning of base-metal thermocouples should be carried out at temperatures well below \(150\,^{\circ }\mathrm{C}\) to avoid erasure of strain effects or imprinting of new thermal signatures.     

Effect of annealing treatment on optical properties and microstructural variation of $$\hbox {WO}_{3}/\hbox {Ag}/\hbox {WO}_{3}$$ multilayer nano-films

Structural and optical properties of \(\text {WO}_{3}/\text {Ag}/\text {WO}_{3}\) nano-multilayer composites were investigated for heat mirror applications. \(\text {WO}_{3}/\text {Ag}/\text {WO}_{3}\) thin films were fabricated through a physical vapour deposition method by using electron-beam evaporation at the vacuum chamber at 10\(^{-5}\) Torr. \(\text {WO}_{3}\) nano-layer was fabricated at 40 nm. Annealing treatment was carried out at 100, 200, 300 and 400\(^{\circ }\)C for 1 h after the deposition of first layer of \(\text {WO}_{3}\) on the glass. On \(\text {WO}_{3}\) film, Ag nano-layers with 10, 12 or 14 nm thickness were deposited. Individual layers morphology was investigated using atomic force microscopy (AFM) and deduced that a smoother layer can be achieved after the annealing at 300\(^{\circ }\)C. Ellipsometry analysis was executed to determine both layers, Ag film thickness and inter-diffusion between the \(\text {WO}_{3}\)–Ag–\(\text {WO}_{3}\) layers. It was inferred that there was almost no interfering among the \(\text {WO}_{3}\)–\(\text {WO}_{3 }\) layers in the samples with 12 and 14 nm Ag thickness; while silver was deposited on the annealed \(\text {WO}_{3}\) layer at 300\(^{\circ }\)C. UV–visible spectrophotometer showed that the annealing treatment of the first \(\text {WO}_{3}\) layer enhanced the transparency of films in the visible region. The innovations of the present study have been based on the annealing of the films and finding an optimum thickness for the Ag film at 12–14 nm. Heat mirrors efficiency was assessed according to the principle of their optical behaviour and optimum performance obtained for 14 nm of Ag film, deposited on annealed tungsten oxide at 300\(^{\circ }\)C.     

Macroscopic Thermal Rectification Device Using Vanadium Dioxide Thin Film

A thermal rectifier is a device in which heat flows in the forward direction but very little can flow in the opposite direction. Because the heat current can be controlled, the device is promising for future practical applications. In this study, the experiments were performed to investigate temperature-gated thermal rectification using macroscopic vanadium dioxide \((\hbox {VO}_{2})\) thin films deposited on an asymmetric substrate. The \(\hbox {VO}_{2}\) phase transition, occurred near 340 K, changed both the electrical and thermal properties. Therefore, we used these properties to investigate the thermal rectification. The \(\hbox {VO}_{2}\) thin films were prepared on cover glass substrates by RF sputtering with a \(\hbox {VO}_{2}\) disk target at \(500~{^{\circ }}\hbox {C}\). The morphology of the thin films was investigated. Silver paste and a copper band were used to connect the films with a heater and temperature controller. We observed thermal rectification in the temperature range of T = 310 K–370 K in several film samples obtained with different degrees of asymmetry, deposition times, and post-annealing times. It is found that \(60{^{\circ }}\) triangular-shaped samples have a rectification coefficient of 1.14, and the rectification coefficient is increased with the increasing of the angle. In addition, the two rectangular-shaped samples have the coefficient of 1.06, which could also be enhanced by increasing the ratio of width.     

Fusion Diagrams in the \mathrm{BiBO}_{3}–\mathrm{YbBO}_{3} and \mathrm{Bi}_{4}\mathrm{B}_{2}\mathrm{O}_{9}–\mathrm{YbBO}_{3} Systems

A calculation model of the Gibbs energy of ternary oxide compounds from the binary components was used. Thermodynamic properties of \(\mathrm{Yb}_{2} \mathrm{O}_{3}\) – \(\mathrm{Bi}_{2}\mathrm{O}_{3}\) – \(\mathrm{B}_{2}\mathrm{O}_{3}\) ternary systems in the condensed state were calculated. Thermodynamic data of binary and ternary compounds were used to determine the stable sections. The probability of reactions between the corresponding components in the \(\mathrm{Yb}_{2} \mathrm{O}_{3}\) – \(\mathrm{Bi}_{2} \mathrm{O}_{3}\) – \(\mathrm{B}_{2} \mathrm{O}_{3}\) system was estimated. Fusibility diagrams of systems \(\mathrm{BiBO}_{3}\) – \(\mathrm{YbBO}_{3}\) and \(\mathrm{Bi}_{4} \mathrm{B}_{2} \mathrm{O}_{9}\) – \(\mathrm{YbBO}_{3}\) were studied by physical–chemical analysis. The isothermal section of the phase diagram of \(\mathrm{Yb}_{2} \mathrm{O}_{3}\) – \(\mathrm{Bi}_{2} \mathrm{O}_{3}\) – \(\mathrm{B}_{2} \mathrm{O}_{3}\) at 298 K is built, as well as the projection of the liquid surface of \(\mathrm{BiBO}_{3}\) – \(\mathrm{B}_{2} \mathrm{O}_{3}\) – \(\mathrm{YbBO}_{3}\) .     

Optical spectroscopy of rare earth-doped oxyfluoro-tellurite glasses to probe local environment

\(\hbox {TeO}_{2}\)-based glasses with a general formula \(65\hbox {TeO}_{2}{-}5\hbox {BaF}_{2}{-}30\hbox {ZnF}_{2}\) (TBZ) (in mol%) were prepared by usual melt quenching technique. Three mol% of europium (Eu) or erbium (Er) were added to the prepared glass at the expense of \(\hbox {TeO}_{2}\). Raman, photoluminescence (PL), UV–visible absorption studies were carried out on the glass samples. Raman spectra of the undoped and doped glasses were analysed using the peak shift and the intensity variation along with full width at half-maximum (FWHM). It was found that Eu-doped TBZ glass has a greater tendency towards depolymerizing the glass matrix by influencing the conversion of \(\hbox {TeO}_{4}\) to \(\hbox {TeO}_{3}\) units compared to Er-doped and undoped glasses. PL spectra of the glass samples show emission due to different possible transitions. Position of the peak of the de-convoluted spectra shows the position of the particular Stark component and the FWHM is a measure of the inhomogeneous broadening. The UV–visible absorption spectra are used to calculate the optical density and to determine the band edge of the glass samples by fitting to the Mott equation. It is seen that Eu-doped TBZ glass has a lesser bandgap than that of Er-doped glass.     

Search for Anomalous Temperature Behavior of the Viscosity of Polyethylene Glycol Solutions

Viscometric studies of polyethylene glycol (PEG 35000) aqueous solutions are presented. The temperature and concentration dependences of the PEG solution viscosities were studied in the range from \(10\,^{\circ }\mathrm{C}\) to \(60\,^{\circ }\mathrm{C}\) and \(5\,\mathrm{mg}{\cdot } \mathrm{ml}^{-1}\) to \(50\, \mathrm{mg}{\cdot } \mathrm{ml}^{-1}\) , respectively. The intrinsic viscosity and the Huggins coefficient have been calculated from the data. The results exclude the recently reported anomalous behavior of these quantities. The measured viscosity is also used to estimate the hydrodynamic and gyration radii of the polymers.     

The Improved Superconducting Properties in the Ex-situ Sintered MgB_{2} Bulks with Mg Addition

The ex-situ method to prepare MgB \(_{2}\) superconductors is favorable in terms of bulk density compared to the in-situ method. Since the packing factor of ex-situ MgB \(_{2}\) is higher than that of in-situ MgB \(_{2}\) , a better \(J_{c}\) , even higher than that of in-situ, is naturally expected if strong grain connectivity is achieved. In the present work, ex-situ MgB \(_{2 }\) polycrystalline bulks with Mg addition were prepared by sintering. Combined with phase composition analysis, microstructure observation and superconducting properties measurement, it is found that Mg addition can obviously reduce MgO impurities, accelerate the self-sintering of MgB \(_{2}\) and even promote the formation of sintering necks between MgB \(_{2}\) grains. Consequently, the sintering density and grain connectivity is enhanced, and the \(J_{c}\) is improved across the whole magnetic field in the ex-situ MgB \(_{2}\) sample with Mg addition. Mg addition is a promising and effective way to further enhance \(J_{c}\) of ex-situ MgB \(_{2}\) superconductors.     

Ultrasonic and structural features of some borosilicate glasses modified with heavy metals

A quaternary glass system \(\hbox {Na}_{1.4}\hbox {B}_{2.8}\hbox {Si}_{x}\hbox {Pb}_{0.3-x}\hbox {O}_{5.2+x}\), with 0 \(\le \) x \(\le \) 0.3, was prepared and studied by Fourier transform infrared spectroscopy, density and ultrasonic techniques to debate the issue of the role of \(\hbox {SiO}_{2}\) in the structure of lead alkali borate glasses. The results indicate that \(\hbox {SiO}_{2}\) generates an abundance of bridging oxygen atoms, [\(\hbox {BO}_{4}\)] and [\(\hbox {SiO}_{4}\)] structural units and changes the bonds B–O–B and Pb–O–B to Si–O–Si and B–O–Si. The latter bonds have higher bond strength and higher average force constant than the former bonds. Therefore, the glass structure becomes contracted and compacted, which decreases its molar volume and increases its rigidity. This concept was asserted from the increase in the ultrasonic velocity, Debye temperature and elastic moduli with the increase of \(\hbox {SiO}_{2}\) content. The present compositional dependence of the elastic moduli was interpreted in terms of the electron–phonon anharmonic interactions and the polarization of \(\hbox {Si}^{4+}\) cation. A good correlation was observed between the experimentally determined elastic moduli and those computed according to the Makishima–Mackenzie model.     

Fully Quantum Cross Second Virial Coefficients for the Three-Dimensional He–H_{2} Pair

A recent high-accuracy three-dimensional potential is used to compute the cross second virial coefficient \(B_{12}(T)\) between helium and molecular hydrogen. These calculations fully account for both quantum effects (with the path-integral Monte Carlo method) and the flexibility of the hydrogen molecule. The effect of flexibility is relatively small (only slightly larger than the expanded uncertainty of our results), but the full quantum mechanical approach is essential to obtain correct results at cryogenic temperatures. Values are calculated from 8 K to 2000 K; the uncertainty of the potential is propagated into uncertainties of \(B_{12}\) . Similar calculations are performed for He with the isotopologues D \(_{2}\) , T \(_{2}\) , HD, HT, and DT. Comparison is made with the experimental data for the He/H \(_{2}\) binary, and with the limited data available for He/D \(_{2}\) and He/HD. The calculated \(B_{12}(T)\) ’s are generally consistent with the experimental results, but have lower uncertainties.