Ionic conductivity of sodium beta″-alumina

Measurements of the electrical conductivity of Na ß″-alumina show that the low-temperature activation energies are 0.3337 ± 0.0055 eV for MgO stabilized crystals grown at 1700°C, 0.275 ± 0.015 eV for crystals with the same starting composition position grown at 1650°C, and 0.1716 ± 0.0093 eV for crystals stabilized with ZnO and grown at 1700°C. The conductivities of almost all crystals at 500°C were found to be 1.3 ± 0.6 Ω^?1 cm^?1. In addition to the growth conditions, the presence of a dc electric field, the type of electrode material, the type of conducting ion, and the concentration of stabilizing ion are important in determining the electrical conductivity. These factors are believed to affect the nature of the ordering of vacancies in the ß″-aluminas, leading to variations in the activation energy.     

Magnetostriction and the magnetic phases of single crystal terbium-50% holmium

The c-axis magnetostriction, λ_c, has been measured in terbium-50% holmium in fields up to 2 T between the Néel and Curie temperatures. The magnitude and temperature dependence of λ_c are similar to those previously reported for dysprosium. Detailed strain measurements between the critical field, H_c, which destroys the antiferromagnetic spiral spin structure and the field induced ferromagnetic phase show that the extent of an intermediate fan phase is more limited than previous theoretical analyses have predicted. The difference between the experimental data and strains calculated from theory can be explained only in part by the influence of magnetostry calline anisotropy.     

Possibility for VUV and x-ray tunable atomic lasers

Novel atomic systems may be suitable for the construction of high-frequency tunable lasers. They involve highly excited bound states embedded in the electronic continuum of opposite parity and decaying into it via radiative autoionization (RA). For the newly established 2p^{3 4}S₀ bound state of He⁻, the calculated induced RA cross section is large around λ ≈ 323 Å.     

EPR study of oriented photoexcited triplets of porphyrins and chlorophylls in a liquid crystal

An EPR study of the photoexcited triplet state of porphyrins, Chl a and the covalently linked dimer of Zn pyrochlorophyllide a, in a liquid crystal, is reported The metalloporphyrins interact to form excimers The low intramolecular energy transfer rate in the dimer (? 10⁶s^?1) suggests that the unfolded form predominates.     

A note on the lower-bound nature of the linearized CPMET

It is shown by a simple demonstration that the energy calculated from the linearized version of the coupled-pair many-electron theory (L-CPMET) of ?í?ek is the same as that would be obtained from the lower-bound equation of the wave operator for pair correlations as derived by Goscinski and Sinano?lu. A possible extension of L-CPMET retaining the lower-bound character is also indicated.     

Shock tensors and shock polars

A refraction law for the velocity at an oblique shock in a compressible fluid is derived in dyadic form similar to that for refraction of light rays at an interface. The shock tensor embodies only the assumptions of conservation of mass and equality of tangential velocity components. Given the shock inclination and density ratio, a quadratic equation in the ratio of the flow speeds can be found with flow turning angle as a parameter. Analysis of the two solutions shows that they lie on a circle in the polar plane, a result independent of the equation of state or other conservation laws. If the density ratio is allowed to vary, a pencil of circles is generated in the hodograph plane ; or, equivalently a right, elliptic cone with two nappes appears in the three-space formed when the density ratio coordinate is added at right angles to the hodograph plane. The further requirements that momentum and energy be conserved taken together with weak restrictions on the functional form of the equation of state are sufficient to permit the development of a general theory of shock polars. The allowed shock states are seen to lie on the space curve formed by intersection of a surface called the Hugoniot cylinder with the elliptic cone. The projection of this space curve on the hodograph plane is the shock polar. The theory is applied to the special case of a polytropic gas by way of illustration.     

Nanocarriers as Active Ingredients Enhancers in the Cosmetic Industry—The European and North America Regulation Challenges

“Flawless skin is the most universally desired human feature” is an iconic statement by Desmond Morris. Skin indicates one´s health and is so important that it affects a person’s emotional and psychological behavior, these facts having propelled the development of the cosmetics industry. It is estimated that in 2023, this industry will achieve more than 800 billion dollars. This boost is due to the development of new cosmetic formulations based on nanotechnology. Nanocarriers have been able to solve problems related to active ingredients regarding their solubility, poor stability, and release. Even though nanocarriers have evident benefits, they also present some problems related to the high cost, low shelf life, and toxicity. Regulation and legislation are two controversial topics regarding the use of nanotechnology in the field of cosmetics. In this area, the U.S. FDA has taken the lead and recommended several biosafety studies and post-market safety evaluations. The lack of a global definition that identifies nanomaterials as a cosmetic ingredient is a hindrance to the development of global legislation. In the EU, the legislation regarding the biosafety of nanomaterials in cosmetics is stricter. “The cost is not the only important issue, safety and the application of alternative testing methods for toxicity are of crucial importance as well”.     

Charge transport and lattice defects in CoO

Measurements of the conductivity and the thermoelectric power of CoO at elevated temperatures suggest that the charge carriers (holes) in this material are itinerant carriers and that the nonstoichiometric defects are complex. Both results are in disagreement with conclusions of past studies but in agreement with recent theoretical calculations of the defect structure of the 3d transition metal monoxides.     

Expressions for certain minors and permanents

We provide explicit formulas for the minors of I–A and for per(I–A) where A is a row stochastic matrix.