ABSTRACT
In the quest for finding novel thermodynamically stable, layered, MAB phases promising for synthesis, we herein explore the phase stability of ternary MAB phases by considering both orthorhombic and hexagonal crystal symmetries for various compositions (MAB, M2AB2, M3AB4, M4AB4, and M4AB6 where M = Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, and Co, A = Al, Ga, and In, and B is boron). The thermodynamic stability of seven previously synthesized MAB phases is confirmed, three additional phases are predicted to be stable, and 23 phases are found to be close to stable. Furthermore, the crystal symmetry preference for forming orthorhombic or hexagonal crystal structures is investigated where the considered Al-based MAB phases tend to favour orthorhombic structures whereas Ga- and In-based phases in general prefer hexagonal structures. The theoretically predicted stable MAB phases along with the structural preference is intended to both guide experimental efforts and to give an insight into the stability for different crystal symmetries of MAB phases.
ABSTRACT
BACKGROUND/AIM: A variety of self-tests addressing individual skin cancer risk are available online. These are generally based on self-estimated measures, such as self-rated skin sensitivity to sun exposure, affecting its reliability. The aim of this study was to investigate whether the addition of objective variables, by means of ultraviolet (UV) sensitivity phototesting and nevi count, could be of contributory value for the composition of a comprehensive risk score for skin cancer, and whether the use of such a score could contribute to change of behavior in the sun after assessment of individual risk. PATIENTS AND METHODS: A sample of 70 voluntary participants, all university students, were recruited for the study. The participants rated their sun exposure habits by filling out the Sun Exposure and Protection Index (SEPI) questionnaire, and their skin UV-sensitivity was decided both by self-estimation, using Fitzpatricks's skin type scale, and objectively, by the performance of a UV-sensitivity phototest. Finally, the number of pigmented nevi on the lower arm was counted both by the participants themselves and by a trained observer. A cumulated skin cancer risk score was calculated on the basis on these three variables (sun habits, UV-sensitivity and nevi count), and the outcome compared whether based on the participants' self-assessments or on the objective assessment. The individual risk score, based on objective measures, along with a tailored sun protection advice, was communicated to the participants, and after three weeks they once again filled-out the SEPI part addressing propensity to increase sun protection. RESULTS: The results showed good correlation between the self-assessed and trained observer performed nevi count, but poor agreement between self-estimated and objectively measured skin UV-sensitivity. For the cumulative risk score, the self-performed score was on average slightly lower than its reference, but no systematic difference could be observed. At follow-up, high-risk individuals showed a significant decrease in total SEPI score (p<0.05). CONCLUSION: Objective assessment of nevi count and skin UV-sensitivity might be of significant value when estimating individual skin cancer risk, in order to communicate tailored sun protection advice.
