Electrochemical study on semiconductive properties of the passive film on rebar in concrete

INTRODUCTION Steel rebar embedded in concrete is protectedagainst corrosion by the thin passive film on its sur-face and the physical protection from concrete. Thealkaline environment (pH≥12.5) of the concrete poresolution triggers passivation on the rebar surface andformation of the protective oxide film. The physicaprotection of concrete coverage hinders the invasionof aggressive agents. However, this passivity can bebroken down by local pH loss as a result of concretecracking or the…     

Two-parameter characterization of low cycle, hysteretic fatigue data

The aim of this research is to characterize the development of fatigue damage by means of stress-strain hysteresis. Experiments were conducted on 14 specimens made of cold-finished unannealed AISI 1018 steel. Results demonstrate that the mechanical hysteresis loop areas, when plotted as a function of the number of loading cycles, show significant variations and demonstrate the three principal stages concerning the progress of the fatigue failure--initial accommodation, accretion of damage and terminal failure. These three stages of fatigue are marked by the transitions at cycles N2 and N3. Experimental results show that although fatigue life Nf ranges from 2644 cycles to 108 992 cycles, the ratios of N2/Nf and N3/Nf tend to be stable： N2/Nf=I 0.7%, N3/Nf=91.3%.     

Evaluation of the formula of stress intensity factor K i for semi-elliptical surface crack

The stress-intensity factor (SIF) of the semi-elliptical surface crack in the finite body under extensional stress is sclculated by using the FEM software ANSYS release 5.5. The correction factor M _f of SIF at different point along the front of the crack is determined. The relation between M _f and the semi-elliptical shape a/c, the relative crack depth a/b, the variation of angle ϑ, the relative crack width 2c/w and the relative height-width ratio h/w are calculated respectively. Finally the application range and the modification of the engineering formula about SIF is proposed.     

Stress intensity factors under combined bending and torsion moments

This paper discusses stress intensity factor (SIF) calculations for surface cracks in round bars subjected to combined torsion and bending loadings. Different crack aspect ratios, a/b, ranging from 0.0 to 1.2 and relative crack depths, a/D, ranging from 0.1 to 0.6 were considered. Since the loading was non-symmetrical for torsion loadings, a whole finite element model was constructed. Then, the individual and combined bending and torsion loadings were remotely applied to the model. The equivalent SIF method, F*_EQ, was then used explicitly to combine the individual SIFs from the bending and torsion loadings. A comparison was then carried out with the combined SIF, F*_FE, obtained using the finite element analysis (FEA) under similar loadings. It was found that the equivalent SIF method successfully predicted the combined SIF for Mode I. However, discrepancies between the results determined from the different approaches occurred when F _III was involved. It was also noted that the predicted F*_FE using FEA was higher than the F*_EQ predicted through the equivalent SIF method due to the difference in crack face interactions.     

Applications of water sensitivity in situ remediation at saltwater-freshwater interface

Based on the laboratory experiments with the saltwater and freshwater replacing each other in the level sand column, taking the kaolin, illite, smectite, bivalent hydrargyrum ion (Hg²⁺) and phenol (C₆H₅OH) as examples, this paper studies the applications of water sensitivity in situ remediation in saltwater-freshwater transition zone. In the water sensitivity process, the release and migration of clay minerals can make the hydraulic conductivity (HC) decrease and pollutants remove. A new type of low penetrable or impenetrable purdah can be built by adding clay minerals into the sand media to replace the underground concrete impenetrable wall to prevent seawater intrusion, and a number of the heavy metals and organic pollutants in the sand media can be removed by in situ remediation. The results show that the content of kaolin and illite influences the water sensitivity process slightly, and HC of the sand columns descends from 0.011 cm/s to 0.001 4 cm/s and 0.001 2 cm/s respectively even if the content reaches 12% (weight ratio, sic passim). However, for smectite, HC descends sharply to about 1×10⁻⁸ cm/s when its content reaches 4%, and no water can flow through the sand columns beyond 5%. The particle release and migration processes can remove the Hg²⁺ and C₆H₅OH out of the sand columns efficiently, the removing rate of Hg²⁺ is 31.68% when the freshwater and saltwater are filtered through the sand columns polluted by Hg²⁺, while it is 67.55% when the water sensitivity occurs. With the same method, the removing rates of C₆H₅OH under the fluid flow and water sensitivity are 55.71% and 43.43% respectively. Supported by National Natural Science Foundation of China (No. 40572142). HAN Zhiyong, born in 1976, male, Dr, associate Prof.     

On Turán type inequality with doubling weights andA * weights

LetH _n be the set of real algebraic polynomials of degreen, whose zeros all lie in the interval [−1,1]. The well known Turán type inequalities tell us that forf(x)∈H _n , it holds ‖f′‖≥C√n‖f‖. This note deals with the weighted Turán type inequalities with the weights having inner singularities underL ^p norm for 0<p≤∞. Our results essentially extend the result of Wang and Zhou (2002), and the method used in this paper is simpler and more direct than that of Wang and Zhou (2002). The results and methods have their own values in approximation theory and computation.     

Regular-singular crossings on nonlinear systems with turning point

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碳化再生细骨料对再生混凝土抗压强度的影响

在再生粗骨料取代率为70%的基础上,研究经碳化强化处理的再生细骨料对再生混凝土基本力学性能的影响规律。并与未碳化再生细骨料的情况进行对比,再生细骨料的取代率为0、20%、30%、40%。实验结果表明:再生混凝土抗压强度随再生细骨料取代率提高而减小,碳化再生细骨料可提高再生混凝土抗压强度。     

One and two dimensional chloride ion diffusion of fly ash concrete under flexural stress

A preloading frame is firstly designed to accurately apply external flexural stress to concrete specimens. Then a method is developed to measure one and two dimensional (1D and 2D) chloride ion concentrations at different distances from the surface of concrete under flexural stress. Using this method and the preloading frame, 1D and 2D stress-diffusion is systematically investigated for fly ash concretes made with different fly ash contents (0%, 10%, 20%, 40%, and 60%), and water to binder ratios (0.3, 0.35, and 0.4). The stress accelerating effect on 1D and 2D chloride ion diffusion is also quantitatively analyzed through a comparison between stress-diffusion and nonstress-diffusion. A diffusion accelerating effect caused by external flexural stress can clearly be observed through the comparison. In order to quantify the stress accelerating effect, a stress accelerating factor is proposed in this paper. The relationship between stress accelerating factor and external stress-to-ultimate stress ratio is given as an exponential function. Finally, the process of the initiation, prorogation, and distribution of microcracks on the tensile face of specimen is observed in-situ by using a small-sized loading frame and scanning electron microscope (SEM). The above research provides an insight into chloride attack on the edge reinforcing bars of concrete structures under flexural stress, such as large-span beam and board in the field of civil engineering.     

Family Structure,Family Instability,and Child Psychological Well-Being in the Context of Migration: Evidence From Sequence Analysis in China

This study conceptualizes parental migration as a dynamic family process that exposes children to parental absence and family instability. Using detailed migration histories, this study identifies the left-behind trajectories of rural Chinese children throughout childhood (age 1–12) and examines the impact on psychological well-being (N = 3,961). Results indicate heterogeneity in children’s experience of parental migration, which is characterized by both persistence (prolonged parental absence) and instability (repeated parental migration). A quarter of rural children experienced prolonged parental migration, and for half of these, by both parents. Another 50% of rural children experienced repeated parental migration. Children continuously left behind by both parents and children who experienced substantial family instability both fared worse in psychological development than those in stable two-parent families.     

Properties of vortex system with random columnar defects at zero temperature

The properties of a two-dimensional vortex system with random columnar defects were studied by cooling the vortex system to zero temperature. The vortex lattice became more and more disordered with increasing pinning strengthf _p. At smallf _p, a triangular vortex, lattice away from the pins was observed. The peak of structure factorS(G₀) of the vortex lattice decreased with pinning strengthf _p, which accorded with the finding that the probability of vortex to be pinned increased withf _p. Some of our results agreed with experimental findings. Project supported by the Ministry of Science and Technology of China (NKBRSF-G19990646) and Zhejiang Province Scientific Foundation (199031).     

受外部周期激励的弱阻尼受迫KdV方程的吸引子

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Frontal asymmetry assessed in infancy using functional near-infrared spectroscopy is associated with emotional and behavioral problems in early childhood

Frontal asymmetry (FA), the difference in brain activity between the left versus right frontal areas, is thought to reflect approach versus avoidance motivation. This study (2012–2021) used functional near-infrared spectroscopy to investigate if infant (M_age = 7.63 months; N = 90; n = 48 male; n = 75 White) FA in the dorsolateral prefrontal cortex relates to psychopathology in later childhood (M_age = 62.05 months). Greater right FA to happy faces was associated with increased internalizing (η² = .09) and externalizing (η² = .06) problems at age 5 years. Greater right FA to both happy and fearful faces was associated with an increased likelihood of a lifetime anxiety diagnosis (R² > .13). FA may be an informative and early-emerging marker for psychopathology.     

Effects of La^3＋on microwave dielectric properties of（Pb0.5Ca0.5）（Fe0.5Ta0.5）O3ceramics

This work investigated the microwave dielectric properties of A-site substitution by rare earth La3+in(Pb0.5Ca0.5)(Fe0.5Ta0.5)O3(PCFT) system.A single perovskite phase was obtained only when the doping content was 2%.Suitable La3+ doping improved microwave dielectric performances.Excessive La3+doping caused the formation of secondary phase,which resulted in the decreasing of permittivity εrand quality factor Qfvalues.Especially,when the doping content is 2%-5%,permittivity εrwas above 75 and Qfvalues were 6...     

The Achievement Motives Scale (AMS): theoretical basis and results from a first try‐out of a Czech form

The achievement motive concept refers to a relatively stable personality characteristic in terms of a capacity to anticipate affects in achievement situations. The motive to achieve success (M _s ) refers to the individual's capacity to anticipate positive affects, and the motive to avoid failure (M _f ) refers to a capacity to anticipate negative affects in achievement situations. Based, among other things, on the conceptualizations of motives, a measurement was constructed to tap the two aspects (M _s and M _f ) of motivation. Over the years the scale has been translated to several languages and used in a number of studies. The Czech version of the scale is an adapted translation of the English one, and was administered to 179 pupils in the sixth grade in 1989. Further, the subjects were retested after an interval of 12 weeks. The analyses indicate that the psychometric properties of the Czech version of AMS are promising.     

Study of the behaviour of the dielectric constant in Cu,Fe：BaTiO3

In this work we study the behaviour of the dielectric constant of BaTiO3 single crystals doped with Cu and Fe for different ion percentages, particularly, the influence of these hetemvalent substitutions on the ferroelectric-paraelectric phase transition whose temperature is found at Tc=120℃ for pure samples. The dielectric constant e in terms of temperature shows that the Curie temperature decreases when the quantity of impurities increases and presents a broadening and flattering of the maximum oft（T） within higher values, with the transition becoming more and more diffuse. It is interesting to have a material with very high permittivity （high-k） because of its capacity to store an important quantity of electric charges. The t anisotropy and the Curie-Weiss law are also verified with a good ratio between the slopes ofε^-l（T） from both sides of the transition, leading to a Curie constant： C= 13 × 10^4 K for BaTiO3：1.6%Fe in the polar phase. BaTiO3 is a displacive ferroelectric going through a first-order phase transition. The substitutions have an effect on the dynamics of the perovskite lattice. They induce charges transfer to Ti and a diminution of elastic forces in BaTiO3. Then we discuss the transition but on the nature of the material. fact that the maximum of permittivity does not depend on the phase     

Parental educational aspirations and children’s academic self-concept: Disentangling state and trait components on their dynamic interplay

The dynamic interplay of parental educational aspirations and children's academic self-concept was examined from late childhood through mid-adolescence within a transactional socialization framework. Parental and child data were gained from a representative Swiss sample within 3-year intervals (N_T1 = 1118; 51% females; 28% migration background; M_{age T1} = 9.26, M_{age T2} = 12.14, M_{age T3} = 15.32). Results from a random intercept cross-lagged panel model revealed positive associations between the two constructs at the between- and within-person level. Findings showed general and time-specific associations between children and parents and reciprocal spill-over effects, whereby higher than usual aspirations predicted higher than usual academic self-concept over time and vice versa, highlighting transactional processes in the context of educational transitions.     

The estimation of the IRT reliability coefficient and its lower and upper bounds, with comparisons to CTT reliability statistics

The primary purpose of this study is to investigate the mathematical characteristics of the test reliability coefficient ρ _XX′ as a function of item response theory (IRT) parameters and present the lower and upper bounds of the coefficient. Another purpose is to examine relative performances of the IRT reliability statistics and two classical test theory (CTT) reliability statistics (Cronbach’s alpha and Feldt–Gilmer congeneric coefficients) under various testing conditions that result from manipulating large-scale real data. For the first purpose, two alternative ways of exactly quantifying ρ _XX′ are compared in terms of computational efficiency and statistical usefulness. In addition, the lower and upper bounds for ρ _XX′ are presented in line with the assumptions of essential tau-equivalence and congeneric similarity, respectively. Empirical studies conducted for the second purpose showed across all testing conditions that (1) the IRT reliability coefficient was higher than the CTT reliability statistics; (2) the IRT reliability coefficient was closer to the Feldt–Gilmer coefficient than to the Cronbach’s alpha coefficient; and (3) the alpha coefficient was close to the lower bound of IRT reliability. Some advantages of the IRT approach to estimating test-score reliability over the CTT approaches are discussed in the end.     

Structure and Magnetic Properties of Fe1-xCx Solid Solution Prepared by Mechanical Alloying

Supersaturated solid solutions Fe1-xCx （0≤x≤0.9 ） of wide composition range have been prepared by mechanical alloying process. Nanocrystalline phase was formed for 0 ≤ x ≤ 0.67 and a large grain phase for 0.75 ≤ x ≤ 0.9. The large fraction of graphite volume puts off formation of nanocrystalline phase for high carbon content. In the large grain phase, magnetization follows simple magnetic dilution, and eoereivity He is mainly due to dissolution of carbon at grain boundaries. In the nanocrystalline phase the alloying effect of carbon is revealed by a distinct reduction of average magnetic moment. The increasing lattice constant with increasing carbon content is observed for x ≤ 0.5, suggesting that the high carbon concentration may enhance diffusion of carbon into the Fe lattice. It shows a discontinuity in the Hc variation with a grain size D of nanocrystalline phase. For small grain D below the critical value, Hc increases with D. For a large grain D, Hc decreases with increasing D. The solubility limit of carbon in a-Fe extended by nanocry- stalline phase formation is discussed.     

Preparation and Dynamic Tensile Behavior of C200 Green Reactive Powder Concrete

A new type of green reactive powder concrete (GRPC) with compressive strength of 200 MPa is prepared by utilizing composite mineral admixtures, natural fine aggregates, and short and fine steel fibers. The quasi-static mechanical properties (mechanical strength, toughness, fracture energy and interfacial bonding strength) of GRPC specimens, cured in three different types of regimes, are investigated. The experimental results show that the mechanical properties of the C200 GRPC made with the powder binders that is composed of 40% of Portland cement, 25% of ultra fine slag, 25% of ultra fine fly ash and 10% of silica fume are better than the others'. The corresponding compressive strength, flexural strength and fracture energy are more than 200 MPa, and 30 000 J/ m2 respectively. The dynamic tensile behavior of the C200 GRPC is also investigated through the split Hopkinson pressure bar (SHPB) according to the spalling phenomenon. The dynamic testing results demonstrate that strain rate has an important effect on the dynamic tensile behavior of GRPC. With the increase of strain rate, its peak stress and relevant strain increase. The GRPC exhibits an excellent strain ratio stiffening effect under the dynamic tensile load with high strain ratio, resulting in a significant change of the fracture pattern.