Synthesis,transformation and superconductivity of dual phase In–Sn alloy nanoparticles embedded in an Al matrix

We report the synthesis of nanoembedded biphasic alloy particles of In–Sn near eutectic alloy compositions embedded in an aluminium matrix by rapid solidification processing. Detailed transmission electron microscopy indicates that the two phases present at room temperature in as-synthesized samples are β and γ phases with tetragonal and hexagonal crystal structures, respectively. These co-exist with a small amount of single phase In or Sn particles with sizes less than 10?nm. Low temperature magnetization measurements indicate a superconducting transition temperature of 5?K, suggesting complete decomposition of the β-phase at small sizes and at low temperature. The small particles show type II behavior with a critical field Hc₁≈44?G and two values for Hc₂ of 250 and 1000?G, respectively. These values are considerably lower than those observed in bulk In–Sn alloys.     

Dendrite growth velocity in the undercooled melt of glass forming Ni50Zr50 compound

Glass-forming Ni₅₀Zr₅₀ intermetallic compound is containerless undercooled and solidified using electrostatic levitation. Large undercoolings up to ?T = 300 K are achieved. The dendrite growth velocity of the congruently melting alloy is measured as a function of undercooling using a high-speed camera technique. The experimental data is analysed within a sharp interface theory. It is found that the driving force of crystallisation is controlling the growth kinetics at ?T < 250 K but at larger undercoolings the growth kinetics is progressively controlled by atomic diffusion. This leads to a slowing down of the growth velocity. The maximum velocity and the temperature at which the maximum occurs (T_max) are inferred from the dendrite growth velocity – undercooling relation. The relation of the temperature T_max and the glass temperature fits into a general classification scheme for glass-forming systems. The kinetic and thermal undercooling terms are calculated within dendrite growth theory as a function of the total undercooling. At ?T > 126 K, the kinetic undercooling dominates and increases rapidly with the undercooling ?T. The maximum prefactor of the kinetic undercooling is plotted vs. the reciprocal temperature. Its temperature dependence is discussed.     

Electropulsing-induced strengthening of steel at high temperature

Electropulsing usually promotes a metastable phase to evolve towards its equilibrium state. This work reports an alternative case, where electropulsing promotes the decomposition of the stable δ-phase in duplex stainless steel at high temperature. This decomposition enables both the γ-phase and the σ-phase in the steel to survive and hence to strengthen it at high temperature. The hardness of the quenched sample with electropulsing treatment is 49.4% higher than that without electropulsing treatment. A fundamental understanding of the observation is developed.     

Analysis of the relation between structure and the superconducting transition in YBa2 Cu3 O∼7

Abstract

It is shown that in the high-T_c YBa₂ Cu₃ O_～7 superconductor the critical temperature is a function of the orthorhombic distortion (b–a)/a of the unit cell. From the extrapolation of the (b - a)/a ratio against T_c , a maximum critical temperature of 66 K for the tetragonal phase of YBa₂ Cu₃ O_～7 was predicted. From the correlation between the transition width δT_c and the orthorhombic distortion there was deduced an upper limit for T_c , in the orthorhombic phase of YBa₂ Cu₃ O_～7 of 94·5K.     

Effects of temperature and electron energy on the electron-irradiation-induced decomposition of sapphire

The effects of temperature and electron energy on the electron-irradiation-induced decomposition of sapphire have been investigated by in situ transmission electron microscopy (TEM). It was found that the decomposition rate of α-Al₂O₃ increased with increasing irradiation temperature and decreased with increasing acceleration voltage. The core-hole Auger decay process (K–F model), rather than knock-on displacement, is responsible for the decomposition of α-Al₂O₃ under electron irradiation.     

Frank–Read sources and the yield of anisotropic cubic crystals

Frank–Read sources are among the most important mechanisms of dislocation multiplication, and their operation signals the onset of yield in crystals. We show that the critical stress required to initiate dislocation production falls dramatically at high-elastic anisotropy, irrespective of the mean shear modulus. We hence predict the yield stress of crystals to fall dramatically as their anisotropy increases. This behaviour is consistent with the severe plastic softening observed in α-iron and ferritic steels as the α ? γ martensitic phase transition is approached, a temperature regime of crucial importance for structural steels designed for use in future nuclear applications.     

Solid-phase epitaxy of implanted silicon at liquid nitrogen and room temperature induced by electron irradiation in the electron microscope

Abstract

Electron-beam-induced solid-phase epitaxy (SPE) has been obtained on cross-sections of implanted Si layers, by in situ irradiation in the electron microscope, with electrons of energies of 200, 250 and 300 keV, at both room and liquid-nitrogen temperature. The, absence of a transition from SPE to layer-by-layer amorphization (which is observed during ion-beam irradiation on decreasing the temperature below a certain critical value) and the athemal nature of the electron-induced crystallization process below room temperature, indicate that, although elastic displacement is the basic mechanism of both processes, the models which describe ion-beam-induced epitaxy in the temperature range 200≤T≤400°C cannot be extrapolated to explain the results of electron irradiation below room temperature.     

The fatigue limits of copper single crystals cyclically deformed at constant plastic strain amplitudes

Based on systematic surface observations, experimental measurements on the fatigue limits of differently oriented copper single crystals cyclically deformed at constant plastic strain amplitudes are summarized, and an orientation dependence of the fatigue limit is sketched. It was found that the fatigue limits of crystals depend mainly upon the low-strain-amplitude dislocation structures, which are characteristic of the particular crystal orientations. When multiple-slip deformation is the main mode of deformation and ultimately produces stable lowenergy dislocation structures such as labyrinth and cell structures, the fatigue limit can be improved notably.     

TUR(BANNED) MASCULINITIES: Terrorists,Sikhs, and trauma in Indian cinema

This paper looks at two noteworthy cinematic representations of events in Punjab in the last two decades. The films Maachis and Hawein are important in the severely limited subsection of films on Punjab. A critical reading of these films throws up many conflicted junctures of representation, political commentary, historical envisioning, and gendered narratives. Both films tend not to engage with the larger political questions and remain sequestered in microcosmic renditions of the events, which, though necessary, continue to represent Punjab, the insurgency or the riots, as isolated events of a larger national history rather than defining moments which point to the very instability of the nation.     

Planar faults in MoSi2 single crystals deformed at high temperatures

Abstract

Dislocation structure and planar faults have been examined in MoSi₂ single crystals deformed at high temperatures. Pure stacking faults were found in a crystal deformed at 900°C. The formation of the stacking fault is closely related to the phase stability of the C11_b and C40 ordered structures. Profuse stacking faults with increasing deformation temperature assist the ductility improvement of the MoSi₂ above about 1200°C. The critical resolved shear stress for {110}(331) and {013}(331) slip is determined in the temperature range 1000 to 1500°C.     

Judgments of Processing Load in Japanese: The Effect of NP-ga Sequences

This study reports an effect of more than two consecutive noun phrases (NPs) with the same nominative case marker, -ga, on ratings of processability for Japanese multiply center-embedded sentences. The findings imply that the processing overload theory of Babyonyshev and Gibson (1995) requires modification. Although that theory sets the critical limit (beyond which parser breakdown occurs) at four processing load units (PLUs), it appears that the parser is overloaded by anything over five PLUs. where a three NP-ga sequence contributes roughly an additional PLU to processing cost. The evidence also suggests that inherently cased NPs are not cost free.     

Solid-solution hardening in dilute and concentrated alloys

Abstract

Numerical analysis of the temperature dependence of the critical resolved shear stress of several binary copper-based alloy single crystals containing 0·11 to 7·6 at.% Mn, 0·01 to 14·0 at.% Al, 0·5 to 8·0 at.% Ge and 5 to 30 at.% Zn, has been carried out in terms of the kink-pair formation model of solid-solution hardening. Several solute atoms are found to be involved in the unit activation process not only in concentrated alloys but also in dilute ones. A single mechanism of solution hardening, which involves the interaction between a dislocation and many solute atoms, is therefore operative in all the alloys referred to above.     

Effect of heterogeneous solute distribution on the anomalous thermomechanical response of Cu–Ni alloy single crystals below 50 K

The anomalous temperature dependence of the critical resolved shear stress (CRSS) of Cu–Ni alloys observed below a certain temperature, T _o?=?50?K, has been accounted for by introducing a stress-concentration factor f(T)?=?[(T?′?+?T _o)/(T?′?+?T)] in the monotonic CRSS–T formulation of the kink-pair nucleation model of solid-solution hardening. The empirical constant T?′ is found to depend not only on the solute concentration, c, but also on the nature of the solute distribution in the host lattice. It is found that the solute distribution is random for c?≤?14 at.% Ni in the Cu lattice and for c?≤?20 at.% Cu in the Ni lattice, whereas some sort of local ordering occurs for all other values of solute concentration.     

Reaction of a Ni-coated Al nanoparticle to form B2-NiAl: A molecular dynamics study

The kinetic reaction in a Ni-coated Al nanoparticle with equi-atomic fractions and diameter of approximately 4.5 nm is studied by means of molecular dynamics simulation, using a potential of the embedded atom type to model the interatomic interactions. First, the large driving force for the alloying of Ni and Al initiates solid state amorphization of the nanoparticle with the formation of Ni₅₀Al₅₀ amorphous alloy. Amorphization makes intermixing of the components much easier compared to the crystalline state. The average rate of penetration of Ni atoms can be estimated to be about two times higher than Al atoms, whilst the total rate of inter-penetration can be estimated to be of the order of 10^?2 m/s. The heat of the intermixing with the formation of Ni₅₀Al₅₀ amorphous alloy can be estimated at approximately ?0.34 eV/at. Next, the crystallization of the Ni₅₀Al₅₀ amorphous alloy into B2-NiAl ordered crystal structure is observed. The heat of the crystallization can be estimated as approximately ?0.08 eV/at. Then, the B2-NiAl ordered nanoparticle melts at a temperature of approximately 1500 K. It is shown that, for the alloying reaction in the initial Ni-coated Al nanoparticle, the ignition temperature can be as low as approximately 200 K, while the adiabatic temperature for the reaction is below the melting temperature of the nanoparticle with the B2-NiAl ordered structure.     

Effect of Si on the formation and stability of the icosahedral quasicrystalline phase in Al–Fe–Cr–Ti alloys

The formation and stability of the quasicrystalline icosahedral (i) phase in melt-spun Al_{93– x} Fe₃Cr₂Ti₂Si _x (x?=?0–5) ribbons are reported. Samples were characterized by X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. Primitive (P-type) ordered i phase particles were found to be homogeneously distributed in an fcc α-Al matrix in the as-melt-spun ribbons. The size of the i phase particles decreased and their thermal stability increased with increasing substitution of Al by Si. The i phase had a decomposition temperature of approximately 480°C in an Al₉₃Fe₃Cr₂Ti₂ ribbon whereas that in an Al₉₂Fe₃Cr₂Ti₂Si₁ ribbon was approximately 500°C. The i phase particles are resistant to coarsening prior to decomposition into crystalline phases. The presence of a small quantity of Si (up to 1.0?at.%) is beneficial to both the thermal stability and the hardness of nanoquasicrystalline Al–Fe–Cr–Ti alloys.     

Light emission from ferroelectric barium titanate nanocrystals

Thin laminates (thickness δ = 20–45 nm) of barium titanate, BaTiO₃ (BT), have been synthesised by the sol–gel method followed by heating of the amorphous precursor powder in air. An orthorhombic BT polymorph forms along with a tetragonal phase (t-BT) after 2 h of heating the precursor at 600°C, as evidenced by a well-defined X-ray diffraction pattern. The average crystallite size D ～ 21 nm compares the δ-value obtained from the scanning electron micrograph. On heating at temperatures as high as 750°C, the structure remains mostly t-BT (D ? 44 nm), which emits violet–blue–green light at a wavelength of 380–580 nm with a maximum at around 422 nm. The emission extends to wavelengths shorter than ～300 nm owing to a quantum-size effect in smaller crystals processed at lower temperatures. Electron paramagnetic resonance (EPR), which occurs at a g-value of 1.995 (linewidth ΔH = 1.12 mT) in a sample heated at 400°C, shows an order of magnitude of lower intensity at g = 1.993 (ΔH = 3.69 mT) on annealing out the paramagnetic defects at 600°C in air. No EPR signal arises in t-BT free from such defects in larger crystals.     

A study of the fcc (FeCo) 23 B 6 phase in fully crystallized Fe-Co-Nb-B-Cu alloys

Fe-Co-Nb-B-Cu alloys lose their nanocrystalline microstructure at a second crystallization process in which (FeCo) 23 B 6 crystals appear as the main boride phase. In this work the structural characteristics and composition of this phase are studied. The amount and grain size of the (FeCo) 23 B 6 phase increase as the Co content in the alloy increases. After recrystallization, f -FeCo crystals remain at a nanometric size. The lattice parameter and Curie temperature of the (FeCo) 23 B 6 phase are reported.     

Affective variability in depression: Revisiting the inertia–instability paradox

How can depression be associated with both instability and inertia of affect? Koval et al. (2013, Emotion, 13, 1132) showed that this paradox can be solved by accounting for the statistical overlap between measures of affect dynamics. Nevertheless, these measures are still often studied in isolation. The present study is a replication of the Koval et al. study. We used experience sampling data (three times a day, 1 month) of 462 participants from the general population and a subsample thereof (N = 100) selected to reflect a uniform range of depressive symptoms. Dynamics measures were calculated for momentary negative affect scores. When adjusting for the overlap among affect dynamics measures, depression was associated with ‘dispersion’ (SD) but not ‘instability’ (RMSSD) or ‘inertia’ (AR) of negative affect. The association between dispersion and depression became non‐significant when mean levels of negative affect were adjusted for. These findings substantiate the evidence that the presumed association between depression and instability is largely accounted for by the SD, while the association between dispersion and depression may largely reflect mean levels of affect. Depression may thus not be related to higher instability per se, which would be in line with theories on the adaptive function of moment‐to‐moment fluctuations in affect.     

Spiritual pathology and religious coping as predictors of forgiveness

Spiritual pathology, religious coping, and dispositional forgiveness were investigated in two studies with graduate students at a Christian university-based seminary. Spiritual pathology was operationalised using measures of spiritual instability and spiritual grandiosity. Study 1 (N?=?194) examined patterns of correlation between positive and negative religious coping items, spiritual pathology, and dispositional forgiveness. Spiritual instability correlated with numerous positive and negative religious coping items while spiritual grandiosity did not. Dispositional forgiveness correlated with more positive than negative religious coping items. Study 2 (N?=?214) tested regression models with these variables. Spiritual grandiosity showed a significant quadratic (concave down) effect in predicting dispositional forgiveness while the linear effect was not significant. A hierarchical regression model showed positive religious coping, spiritual instability, and the quadratic effect for spiritual grandiosity each predicted unique variance in dispositional forgiveness after controlling for spiritual impression management. Negative religious coping was not related to dispositional forgiveness when included with these variables.