Critical state behaviors of a coarse granular soil under generalized stress conditions

Critical state line (CSL) is the central concept in soil mechanics. A series of true triaxial compression tests under the constant-\({p}'\) and constant-b loading condition were carried out to investigate the CSL of a coarse granular soil. It was observed that the intermediate principal stress ratio (i.e., the b-value) greatly influenced the CSLs in both \(q{-}{p}'\) and \(e{-}{p}'\) spaces. The CSL slope in the \(q{-}{p}'\) space decreased with an increase in b-value. The intercept and gradient of the CSL in the \(e{-}{p}'\) space decreased with increasing b-value. CSLs incorporating the effects of the b-value in \(q{-}{p}'\) and \(e{-}{p}'\) spaces were extended to three-dimensional critical state surfaces (TCSSs) in \(q{-}{p}'{-}b\) and \(e{-}{p}'{-}b\) spaces. Two empirical equations were proposed for the two TCSSs in \(q{-}{p}'{-}b\) and \(e{-}{p}'{-}b\) spaces, respectively. The predictions by the two equations were in good agreement with the corresponding experimental data. The relationship between the excess friction angle (the difference between the peak state and critical state friction angles) and initial state parameter was influenced by the b-value. However, the relationship between the maximum dilatancy and initial state parameter was independent of the b-value.     

Microstructure and mechanical properties of accelerated sprayed concrete

Considering the different hydration processes of concrete without accelerator, sprayed concrete with low-alkali accelerator not only presents short setting times and high early-age mechanical properties but also yields different hydration products. This study presents an analysis of the mechanical properties of concrete with and without accelerator and sprayed concrete with three water–binder (w/b) ratios and four dosages of fly ash (FA) after different curing ages. It also examines the setting time, mineral composition, thermogravimetric–differential scanning calorimetry curves and microscopic images of cement pastes with different accelerator amounts. Furthermore, the setting time and microstructure of accelerated sprayed concrete with different w/b ratios and FA contents are examined. Results show that the retarded action of gypsum disappears in the accelerated cement–accelerator–water system. C₃A is quickly hydrated to form calcium aluminate hydrate (CAH) crystals, and a mesh structure is formed by ettringite, albite and CAH. A large amount of hydration heat improves the hydration rate of the cement clinker mineral and the resulting density, thereby improving mechanical properties at early curing ages. The setting times of the pastes increase with increasing w/b ratio and FA dosage. Thus, the hydration level, microstructure and morphology of the hydration products also change. Models of mechanical properties as functions of w/b, FA and curing age, as well as the relationship between compressive strength and splitting tensile strength, are established.     

Effect of γ-irradiation on the frequency-independent parameters of an equivalent circuit for two-dimensional island platinum films

Four sets (A, B, C and D) of two-dimensional island platinum films [2D-I(Pt)Fs] were prepared by the thermal evaporation technique. The mass thicknesses for the films of such sets are 1, 5, 10 and 20 Å, respectively. The frequency-independent parameters of one of the equivalent circuit for island metal films in general are R _b, R _g and C _g where R _b is the resistance of the islands themselves while R _g is the resistance that accompanies the transfer of electrons across the gaps among islands and C _g is the capacitance that results from the separated metallic islands. The least-square values of R _b, R _g and C _g for our films were deduced via a computerized analysis. The stabilized films were exposed to γ-rays at doses 100, 200, 300, 500 and 700 Gy using ¹³⁷Cs (0.662 MeV) radiation source of dose rate 0.5 Gy/min. It was found that (1) For any particular mass thickness: (a) R _b and R _g decreases with the increase in the dose of γ-rays while C _g increases (b) the absolute value of the fractional change in R _b, R _g and C _g increases with the increase in dose. (2) For any particular dose the increase in the fractional change in R _b, R _g and C _g becomes more pronounced when the mass thickness increases. Qualitative interpretation for our results was given on the ground that γ-rays changed the island’s shape from spherical to prolate spheroid one and this has been checked experimentally via imaging the films by Atomic Force Microscope before and after γ-irradiations.     

Explanation of Non-linear In-Plane Resistivity and Hall Coefficient in the Normal State of Cuprates: Polaronic Approach

We present a theoretical study of the in-plane resistivity ρ _{a b} (T) and Hall coefficient R _H (T) within the polaronic model and precursor pairing scenario by considering a two-component charge carrier picture in the normal state of high-temperature superconducting cuprates (HTSC). Here, we use a Boltzmann-equation approach and extended BCS-like model to compute ρ _{a b} (T) and R _H (T) in the τ-approximation. The opening of the pseudogap (PG) in the normal state of the cuprates should affect their transport properties. We have found that the transition to the PG regime and the effective conductivity of charge carriers in the normal state are responsible for the pronounced non-linear temperature dependence of ρ _{a b} and R _H . With the two-component model analysis, we conclude that the opening of the BCS-like PG, while the non-linear temperature dependence of ρ _{a b} and R _H could be understood as a consequence of pairing fluctuations in the PG state of cuprate superconductors. The calculated results for ρ _{a b} (T) and R _H (T) were compared with the experimental data obtained for various hole-doped cuprates. For all the considered cases, a good quantitative agreement was found between theory and experimental data. We also show that the energy scales of the binding energies of charge carriers are identified by PG crossover temperature on the cuprate phase diagram.     

Influence of Oxygen on the Tribomechanical Properties of Single Crystals of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">δ</Emphasis></Subscript>

This paper reports a study on the mechanical and tribological properties of ab- and a (b) c?planes of YBa₂Cu₃O_7?δ single crystals. The single crystals were grown using a CuO-BaO self-flux method. The oxygenation effect on the mechanical and tribological properties of ab- and a (b) c?planes is reported. For the ab- plane, the hardness and elastic modulus were around 6 and 50 GPa, respectively. In this case, significant differences were not observed among the hardness and elastic modulus at different oxygenation states. However, the hardness and elastic modulus for as-grown and oxygenated YBa₂Cu₃O_7?δ single crystals were different from that of the a (b) c?plane, and were observed to be slightly higher for the as-grown than for the oxygenated samples. For as-grown and oxygenated samples, we observed hardness values around 4.7 and 2.0 GPa, respectively. Regarding the elastic modulus, the values were 75 and 40 GPa, respectively. The indentation fracture toughness values on the ab- plane for the as-grown and oxygenated YBa₂Cu₃O_7?δ single crystal were 3.7 ± 1.2 and 2.9 ± 1.2 MPa m^1/2, respectively. For the ab- plane, the scratch resistance of the as-grown sample was higher than that of the oxygenated sample and the scratches under load were deeper for the oxygenated sample. As regards the a (b) c?plane, the scar features were seemingly constant through all the scratch lengths and the scratches under load were deeper and larger for the oxygenated than that for the as-grown sample.     

The Use of Acoustic Emission Intensity Analysis for the Assessment of Cover Crack Growth in Corroded Concrete Structures

In this paper, acoustic emission (AE) intensity analysis was utilized to assess the concrete cover cracking due to steel corrosion in reinforced concrete structures. A total of 30 reinforced concrete prism samples were tested under an accelerated corrosion test coupled with continuous AE monitoring using attached AE sensors. The samples were cast with three concrete cover thicknesses (20, 30 and 40 mm) around steel bars and were exposed to five percentages of steel mass loss: 1, 2, 3, 4, and 5 %. The cover cracking was monitored daily by visual inspection to detect and measure crack widths. Different AE signal parameters were continuously recorded during the tests, including number of hits, signal strength, energy, and amplitude. The acquired AE events were subjected to an intensity analysis of signal strength to estimate historic index (H (t)) and severity (\(S_r)\). In addition, a b value analysis was conducted on all AE data and the results were compared to those obtained from the intensity analysis. The results showed that increasing the cover thickness had no significant impact on AE parameters (number of hits, cumulative signal strength, cumulative energy, amplitude, H (t), and \(S_{r})\) at similar values of crack growth. Nonetheless, varying the cover thickness from 20 to 40 mm resulted in lower crack widths and slightly higher b values at the same levels of steel mass loss. It was also found that both H (t) and \(S_r\) showed a more evident correlation with the values of crack growth than did b values, regardless of cover thickness or percentage of steel mass loss. Finally, an intensity classification chart was developed to quantify the cover crack growth based on the values of H (t) and \(S_{r}\).     

The influence of the diffusion cooling on the noise band of the superconductor NbN hot-electron bolometer operating in the terahertz range

Results of an experimental study of the noise temperature (T _n ) and noise bandwidth (NBW) of the superconductor NbN hot-electron bolometer (HEB) mixer as a function of its temperature (T _b ) are presented. It was determined that the NBW of the mixer is significantly wider at temperatures close to the critical ones (T _c ) than are values measured at 4.2 K. The NBW of the mixer measured at the heterodyne frequency of 2.5 THz at temperature T _b close to T _c was ~13 GHz, as compared with 6 GHz at Tb = 4.2 K. This experiment clearly demonstrates the limitation of the thermal flow from the NbN bridge at T _b ? T _c for mixers manufactured by the in situ technique. This limitation is close in its nature to the Andreev reflection on the superconductor/ metal boundary. In this case, the noise temperature of the studied mixer increased from 1100 to 3800 K.     

Formation of Superhard State of the TiZrHfNbTaYN Vacuum–Arc High-Entropy Coating

Complex studies of the formation of the superhard state in the TiZrHfNbTaYN vacuum-arc high-entropy coating were carried out. Based on the approach of the structural surface engineering, the regularities of the formation of the triads composition–structure–physico-mechanical properties depending on the supplied potential displacement are established. It is shown that the increase of U _b at the formation of a coating leads to a decrease of the relative content of a light (Ti) and increase of a heavy (Ta, Hf) metal components, which is determined by radiationally stimulated processes in a near-surface region at the deposition. The formation of the single-phase state (based on the fcc of metal lattice) in the range U _b from–50 to–250 V and revealed the formation of the preferred orientation of the crystallites with the axis [111], which is perpendicular to the growth plane. The increase of the perfection of the texture with the [111] axis with increasing U _b is accompanied with an increase of the coatings hardness, which makes it possible to achieve the superhard state (H = 40.2 GPa) at U _b =–250 V.     

Phenomenological Model of Magnetocaloric Effect in La<Subscript>0.7</Subscript>Ca<Subscript>0.2</Subscript>Ba<Subscript>0.1</Subscript>MnO<Subscript>3</Subscript> Manganite Around Room Temperature

In this work, we studied in detail the magnetic and magnetocaloric properties of the La_0.7Ca_0.2Ba_0.1MnO₃ compound according to the phenomenological model. Based on this model, the magnetocaloric parameters such as the maximum of the magnetic entropy change ΔS _M and the relative cooling power (RCP) have been determined from the magnetization data as a function of temperature at several magnetic fields. The theoretical predictions are found to closely agree with the experimental measurements, which make our sample a suitable candidate for refrigeration near room temperature. In addition, field dependences of \({{\Delta } S}_{\mathrm {M}}^{\max }\) and RCP can be expressed by the power laws \({\Delta S}_{\mathrm {M}}^{\max }\approx a\)(μ ₀ H) ⁿ and RCP ≈b(μ ₀ H) ^m , where a and b are coefficients and n and m are the field exponents, respectively. Moreover, phenomenological universal curves of entropy change confirm the second-order phase transition.     

Structural relationship between random copolyimides and their carbon fibers

A series of polyimide (PI) fibers synthesized from pyromellitic dianhydride (PMDA), 4,4′-oxydianiline (ODA), and p-phenylenediamine (p-PDA) were prepared by a two-step wet-spinning process. The prepared PI fibers were then carbonized with the increasing temperatures up to 1500 °C under a high-purity nitrogen atmosphere. The effects of ODA/p-PDA molar ratios on the chemical structure, microstructure, chain orientation, and structural evolutions of the PI fibers were systematically investigated. The elemental composition, morphology, and aggregation structure after carbonization were also analyzed. The results showed that different chemical compositions have greatly influenced the aggregation structures of the resulting PI and carbon fibers. The PI fibers showed increased crystallinity and orientation degree with the decreased ODA moieties, while the corresponding PI-based carbon fibers (CFs) exhibited perfect graphitic structures. The CFs derived from PMDA/p-PDA PI backbone with flat chains exhibited a well-defined graphite structure with d ₀₀₂ of 0.349 nm and I _D/I _G of 1.442. In addition, the carbon yield of the prepared PI-based carbon fibers reached more than 95 %.     

Crystal structure of the low-temperature forms of cesium and rubidium orthophosphates

The crystal structure of the low-temperature forms of the Cs₃PO₄ and Rb₃PO₄ orthophosphates has been determined for the first time by neutron diffraction using the Rietveld method. Cs₃PO₄ and Rb₃PO₄ are shown to be isostructural with K₃PO₄: orthorhombic cell (sp. gr. Pnma, Z = 4); lattice parameters a = 1.23177(6) nm, b = 0.88948(4) nm, c = 0.64197(3) nm for Cs₃PO₄; a = 1.17362(2) nm, b = 0.81046(1) nm, c = 0.615167(9) nm for Rb₃PO₄.     

Influence of moisture condition on chloride diffusion in partially saturated ordinary Portland cement mortar

Experiments have been carried out to study the influence of moisture condition, including moisture content and its distribution, on the chloride diffusion in partially saturated ordinary Portland cement mortar. The mortar samples with water-to-cement (w/c) ratios of 0.4, 0.5 and 0.6, cured for 1 year, were preconditioned to uniform water saturations ranging from 18 to 100%. The interior relative humidities of these partially saturated cement mortars, i.e. water vapour desorption isotherm (WVDI), were measured. The WVDI results in relation to the pore structures obtained from the mercury intrusion porosimetry tests of paste samples with the same w/c ratios were analyzed, which provided a basic insight into the moisture distribution in the non-saturated cement mortars. The relative chloride diffusion coefficients of cement mortars at various water saturations were determined based on the Nernst-Einstein equation and conductivity technique. It is found that the relative chloride diffusion coefficient D_rc depends on the degree of water saturation S_w and WVDI. At a given S_w level, the D_rc is larger for a higher w/c ratio. The role of the w/c ratio in the D_rc–S_w relation, however, becomes less pronounced with increasing w/c ratio. There exists a critical saturation, below which the water-filled capillary pores are discontinuous and the D_rc-value tends towards infinitely small. An increase of the w/c ratio results in a decrease of the critical saturation level.     

Very high thermal stability with excellent dielectric,and non-ohmics properties of Mg-doped CaCu<Subscript>3</Subscript>Ti<Subscript>4.2</Subscript>O<Subscript>12</Subscript> ceramics

In this work, the nominal CaCu_3?xMg_xTi_4.2O₁₂ (0.00, 0.05 and 0.10) ceramics were prepared by sintering pellets of their precursor powders obtained by a polymer pyrolysis solution method at 1100 °C for different sintering time of 8 and 12 h. Very low loss tangent (tanδ)?<?0.009–0.014 and giant dielectric constant (ε′) ～?1.1?×?10⁴–1.8?×?10⁴ with excellent temperature coefficient (Δε′) less than ±?15% in a temperature range of ??60 to 210 °C were achieved. These excellent performances suggested a potent application of the ceramics for high temperature X8R and X9R capacitors. It was found that tanδ values decreased with increasing Mg²⁺ dopants due to the increase of grain boundary resistance (R_gb) caused by the very high density of grain, resulting from the substitution of small ionic radius Mg²⁺ dopants in the structure. In addition, CaCu_3?xMg_xTi_4.2O₁₂ ceramics displayed non-linear characteristics with the significant enhancements of a non-linear coefficient (α) and a breakdown field (E_b) due to Mg²⁺doping. The high values of ε′ (14012), α (13.64) and E_b (5977.02 V/cm) with very low tanδ value (0.009) were obtained in a CaCu_2.90Mg_0.10Ti_4.2O₁₂ ceramic sintered at 1100 °C for 8 h.     

Synthesis and Superconductivity of Layered Compounds with Orthogonal [Zr<Subscript>2</Subscript>N<Subscript>2</Subscript>] Network

Layered α-form ZrNX (X: Cl and Br) compounds with high quality were prepared by chemical vapor transport. The intercalation of alkali metal A (A: Li, Na, K, Rb) was carried out to realize electron doping into the orthogonal [Zr₂N₂] layers. The Rietveld refinement analysis reveals that the [Zr₂N₂] crystalline layers in the intercalation compounds shift mutually in the ab plane when compared with the hosts. Magnetic measurements show that the intercalation compounds A _x ZrNX are changed into superconductors with transition temperature T _c of up to 12 K. Upon the cointercalation of solvent molecules such as THF, T _c decreases to as low as 6.1 K with increasing the interlayer spacing d up to 14 Å, which is similar to the d dependence of T _c recently found in electron-doped α-form TiNX series. We also succeeded in synthesizing another new polymorph of α-Zr₂N₂S by the topochemical reaction between α-form ZrNX and Na₂S. α-Zr₂N₂S (space group: Immm, a = 4.1375(1) Å, b = 3.5422(1) Å, and c = 11.5204(3) Å) has the same α-[Zr₂N₂] layers, whereas the interlayer spacing between two adjacent [Zr₂N₂] layers is effectively decreased by 1/3 when compared with the parent compounds of ZrNX.     

Appearance of Superconductivity at 15.9 K in Layered V<Subscript>2</Subscript>AlN

A bulk polycrystalline sample with the nominal compositions represented by V₂AlN_1?δ was synthesized by a two-step solid-state reaction. The structural characterization has been done via X-ray diffraction, followed by Rietveld refinements, which revealed that the layered V₂AlN is crystalized in cubic Fm3m space group with lattice parameters a = b = c = 6.127 Å. Both DC resistivity and magnetization measurements confirmed that V₂AlN is a bulk superconductor with superconducting transition temperature (T _c ) of 15.9 K.     

Improvement of the Magnetization of Barium Hexaferrites Induced by Substitution of Nd<Superscript>3+</Superscript> Ions for Fe<Superscript>3+</Superscript> Ions

Barium hexagonal ferrites (BaNd _x Fe_12?x O ₁₉) have been synthesized by initial high-energy milling of the precursors and calcining subsequently. The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). XRD and SEM examinations reveal that a high-crystallized hexagonal BaNd _x Fe_12?x O ₁₉ with lamellar morphology is obtained when the precursor is calcined at 1200^°C in air for 3 h. The hexagonal crystalline structure of BaFe₁₂ O ₁₉ is not changed after doping Nd³⁺ ions in BaFe₁₂ O ₁₉. However, lattice parameters a and b values increase with an increase in Nd content at first, then decrease. Nd substitution may improve the magnetic properties of BaNd _x Fe_12?x O ₁₉. BaNd_0.1Fe_11.9 O ₁₉, obtained at 1050^°C, has the highest specific saturation magnetization value (80.81 emu/g) and magnetic moment (16.21 μ _B); BaNd_0.2Fe_11.8 O ₁₉, obtained at 950^°C, has the highest coercivity value, 4075.19 Oe.     

High-temperature behavior and degradation mechanism of SiC fibers annealed in Ar and N<Subscript>2</Subscript> atmospheres

The thermal and mechanical stability of SiC fibers at elevated temperature is an important property for the practical application of SiC fiber-reinforced ceramic matrix composites and is related to the heat-treating atmosphere. In this study, the high-temperature behavior of KD SiC fibers with low oxygen content was investigated in both Ar and N₂ at temperatures from 1400 to 1800 °C through scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Auger electron spectroscopy, resistivity measurements, and tensile tests in order to understand the effects of atmospheres on the degradation of the fibers. The results show that high-temperature treatment caused more severe strength degradation in Ar than in N₂. In particular, the fibers heat treated in N₂ at 1700 °C retained a relatively high strength of 1.52 GPa, 60 % of their original strength, while the fiber strength was completely lost after heat treatment in Ar. Fiber strength degradation was mainly caused by a combination of crystal growth and surface flaws. The formation of huge grains and porosity in the fiber surfaces, owing to the thermal decomposition of the SiC _x O _y N _z and SiC _x O _y phases, significantly degraded the strength for fibers heat treated in Ar. However, the suppressing effect of N₂ on the decomposition of the SiC _x O _y N _z phase in the fiber surfaces and nitrided case on the decomposition of the SiC _x O _y phase in the fiber cores, led to higher SiC fiber temperature stability in N₂ rather than Ar.     

The Effect of Sn Substitution of Pb on Microstructure and Superconducting Properties of Bi–Pb–Sr–Ca–Cu–O Superconductor

The effect of substitution of Pb by Sn in Bi_1.6Pb_0.4?x Sn _x Sr₂Ca₂Cu₃ O _δ samples at x = 0.0, 0.1, 0.2, and 0.3 on the critical transition temperature and structural properties was investigated in this work. All the samples were prepared by the solid-state reaction method. The prepared samples were characterized by X-ray diffraction (XRD), resistance–temperature curve (R–T), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The Sn ⁴⁺ substitution of Pb ²⁺ caused significant changes in the properties of the samples. The formation of the (Bi, Pb)-2212 phase was stabilized and the T _c (onset) was improved at the x = 0.2 level of Sn ⁴⁺ substitution. The SEM micrographs have shown that the structure of the sample with x = 0.2 became more dense. However, samples with x = 0.1 and 0.3 have not shown zero resistance by EDS analysis because of oxygen deficiency.     

Investigation of ITS-90 Inconsistencies in Overlap Region of the Water-indium,Water-tin,and Water-zinc Sub-ranges

One of the significant uncertainties in Standard Platinum Resistance Thermometer (SPRT) calibration by fixed-points method is Type I non-uniqueness (sub-range inconsistencies). Sub-ranges water-tin (W ₉ ) and water-indium (W ₁₀ ) lies in the water-zinc (W ₈ ) sub-range of the International Temperature Scale of 1990. Therefore, three sub-range inconsistencies [W ₈ and W ₉ (SRI _8–9 ), W ₈ and W ₁₀ (SRI _8–10 ), and W ₉ and W ₁₀ (SRI _9–10 )] occur. This paper investigated these inconsistencies using the calibration data of 12 SPRTs from six manufacturers. The result shows that the magnitude of the inconsistency for SRI _8–9 , SRI _8–10 , and SRI _9–10 are about 2.5, 2.2 and 1.8 mK, respectively.