Microwave-dielectric and magnetic properties of Ta-doped BiFeO3 nanopowders

BiFe_{1? x} Ta _x O₃ (x = 0, 0.05, 0.1) nanopowders have been fabricated by a simple sol–gel method. Dielectric measurements at microwave frequencies (2–18 GHz) were made using a vector network analyser. Without tantalum, the BiFeO₃ nanopowder presents a relaxation-like response with a characteristic frequency of 15 GHz, which can be associated with an overdamped process. The Ta-doped nanopowders, however, show resonant behaviour with resonant frequencies of 12.5 and 14.6 GHz. The intensity of the resonant peak near 14.6 GHz decreases with increasing Ta addition. This behaviour is associated with a damped resonance process. Room-temperature magnetic measurements indicate that the addition of Ta influences the magnetic properties of the BiFeO₃ nanopowders, with BiFe_0.95Ta_0.05O₃ having the strongest ferromagnetism with a saturation magnetisation M _s of about 0.05 µ_B/Fe. The origin of the enhanced ferromagnetism is possibly associated with the distortion of the oxygen octahedral by the Ta substitution or/and the statistical distribution of Fe³⁺ and Fe²⁺.     

Stable singular or negative stiffness systems in the presence of energy flux

We report stable systems which exhibit quasistatic stiffness that can be negative or tend to infinity without external constraint. They are based on coupled fields in the non-equilibrium presence of energy flux that is modulated by force. They evade thermodynamic restrictions by relaxing a restrictive assumption: equilibrium. Negative values of physical properties, including compressibility and heat capacity, are considered forbidden in classical thermodynamics; such analyses provide bounds on the stiffness and other properties of multiphase materials. Stable negative and singular stiffness is demonstrated experimentally in a piezoelectric system and in a thermoelastic granular material. Coupled fields occur naturally under a wide range of conditions and form the basis for many forms of technology including sensors, actuators, and electric coolers. Because all materials exhibit at least one coupled field effect, the concept is broadly general and is applicable to attaining extreme values of any physical property e.g. stiffness, permittivity, piezoelectricity.     

Electric transport properties of Pt/Permalloy bilayers in the presence of an external magnetic field

A recent experimental study of the electric properties of Pt/Permalloy bilayers based on a simultaneous application of an in-plane microfrequency current and an external magnetic field is simulated on a fully relativistic ab initio level by considering the resistivity as an implicit function of the free energy. It is found that the oscillations detected experimentally are caused by the different behavior of out-of-plane and in-plane resistivities in the vicinity of that value of the free energy that corresponds to the resonant field induced by the applied current. A necessary precondition for such oscillations is a sizeable perpendicular anisotropy, which is not the case in systems consisting only of Permalloy. It is shown that the observed phenomenon is essentially an interface effect.     

Comparative study of local structure in Zr70Al10Ni20 and quasi-crystal-forming Zr70Al9Ni20Pd1 metallic glasses

The local structure of Zr₇₀Al₉Ni₂₀Pd₁ metallic glass, in which a nano-icosahedral quasi-crystalline phase (I-phase) is formed in the primary stage of crystallization, has been examined and compared with that of Zr₇₀Al₁₀Ni₂₀, the supercooled liquid state of which has a high stability. Since the local environments around the Zr and Ni atoms do not change drastically by the addition of 1 at.% Pd to Zr₇₀Al₁₀Ni₂₀, as evidenced by radial distribution function (RDF) and extended x-ray absorption fine structure (EXAFS) studies, we deduce that the icosahedral phase formed in the Zr₇₀Al₉Ni₂₀Pd₁ metallic glass has a local structure similar to that in Zr₇₀Al₁₀Ni₂₀. Although a very slight rearrangement of Zr–Zr atomic pairs occurs during quasi-crystallization, the I-phase formation is achieved without disturbing the dominant local structure in the glassy state of the Zr₇₀Al₉Ni₂₀Pd₁. An icosahedral local structure is proposed for Zr–Al–Ni metallic glass system as well as for primary quasi-crystal (QC)-forming Zr-based metallic glasses.     

Shear vibration of a crystal plate carrying an array of microbeams

We study shear vibration of a rotated Y-cut quartz crystal plate carrying an array of microbeams with their bottoms fixed to the top surface of the plate. The beams undergo flexural vibrations when the plate is in shear motion. The plate is modeled by the theory of anisotropic elasticity. The beams are modeled by the Euler–Bernoulli theory for beam bending. A frequency equation that determines the resonant frequencies of the structure is derived. An analytical solution on beam-induced frequency shift is obtained using a perturbation procedure. It is shown that the frequency shift may be used to measure geometric/physical properties of the beam array. A vibrating crystal plate carrying a beam array may also be considered for application as an ultrasonic brush.     

Pressure-induced changes in electronic and vibrational properties of LaS

The high-pressure induced phase transition in LaS has been investigated by means of first-principles calculations, and density-functional linear-response theory. A pressure-induced soft-acoustic phonon mode is identified at 30?GPa, which is in favourable agreement with the measured pressure-induced phase transition in LaS from the rocksalt to the CsCl structure. Phonon calculations reveal that pressure-induced instabilities of the transverse acoustic modes at the [?00] and [??0] directions are responsible for the phase transition. Furthermore, it is found that a decrease of bonding for S-p bonds and an increase of anti-bonding for La-d bonds significantly weakens the stability of the rocksalt phase of LaS under pressure, and hence inducing the structural phase transformation.     

Dynamic properties of an ultrafine-grained Mg–Zn–Zr alloy

The effect of ultrafine-grained structure formation in Mg–Zn–Zr alloy ZK60 on its mechanical response was investigated at strain rates ranging from quasi-static to dynamic regimes. The study demonstrated that the strength characteristics of the material rise significantly with increasing strain rate, while its ductility is reduced. These effects are particularly pronounced in the dynamic loading regime, at strain rates in the (1?5)?×?10²?s^?1 range. In the ultrafine-grained alloy ZK60, the energy absorption per unit volume, W, is enhanced by grain refinement by a factor as high as eight for the highest strain rate of 5?×?10²?s^?1 investigated. The analysis is focused on the microstructure features that bring about the observed improvement of the tensile characteristics, as well as the deformation and fracture modes prevalent at different strain rates. The results obtained contribute to the exploration and understanding of dynamic behaviour of magnesium alloys.     

Validation of a Coping Scale in an African Context

The research aims were to compile and validate a multi-dimensional coping measure, taking African-centred coping behaviour into consideration. In a pilot study the Setswana-COPE (S-COPE) and the Africultural Coping Systems Inventory (ACSI) were administered to Setswana-speaking participants (N = 274). Selected items from these measures were combined into a single 35-item measure, the N-COPE, which was administered to another group of Setswana-speaking participants (N = 1050) together with a number of measures of psychological well-being. Reliability coefficients yielded a Cronbach alpha of.74 for the N-COPE total. Criterion-related validity was determined by correlating the N-COPE with other measures of psychological well-being. It was concluded that the N-COPE showed promising results for use in this context, but further refinement and validation is necessary.     

Primitivism and the Analogy between Colors and Values

The analogy between colors and values is strongly interlinked with the idea that these properties are by nature dispositions or response‐dependent properties. Indeed, that colors are essentially visible, and values are inherently motivational, cries out for a dispositional or a response‐dependent account. Recently, Primitivism has challenged the viability of the dispositional account of colors, taking the apple, for instance, to be “gloriously, perfectly, and primitively red.” Unsurprisingly, the attack on the dispositional account of colors has found a moral analogue in the view that values are sui generis irreducibly primitive properties. The question this article addresses is whether given Primitivism the analogy between colors and values is preserved; or in other words, whether Primitivism breaks the bond between the dispositional account and the analogy between colors and values.     

Knowledge ascriptions and the psychological consequences of changing stakes

One of the many ways that ‘deflationary’ and ‘inflationary’ theories of truth are said to differ is in their attitude towards truth qua property. This difference used to be very easy to delineate, with deflationists denying, and inflationists asserting, that truth is a property, but more recently the debate has become a lot more complicated, owing primarily to the fact that many contemporary deflationists often do allow for truth to be considered a property. Anxious to avoid inflation, however, these deflationists are at pains to point out that the truth property, on their view, is not a property of any significant interest. Correspondingly, inflationists have seen this as an opportunity to refine what kind of property they think truth is, which—according to them—moves their views beyond deflationism. The upshot of this is that there are number of different accounts in the literature of what distinguishes an inflationary truth property from a deflationary one, or—as it is sometimes put—what distinguishes a ‘substantive’ property from an ‘insubstantive’ one. This has made it hard to pin down exactly what is at issue at the metaphysical level between deflationists and inflationists, which makes it increasingly hard to see how debates between them are properly phrased. Given that these positions represent the two central attitudes towards truth in contemporary debates, this makes for a serious obstacle for the project of discerning the correct theory of truth. The aim of this paper is to discern the best way to distinguish between substantive and insubstantive properties, and thus to restore some focus to these debates. I argue that the three central distinctions in the literature fail, and offer what I take to be a more promising distinction in terms of a graded distinction between abundant and sparse properties.