Grand Unification without Higgs Bosons

We discuss how a model for the electroweak interactions without a Higgs could be embedded into a grand unified theory. The requirement of a non-trivial fixed point in the SU(2) sector of the weak interactions together with the requirement of the numerical unification of the gauge couplings leads to a prediction for the value of the SU(2) gauge coupling in the fixed point regime. The fixed point regime must be in the TeV region to solve the unitarity problem in the elastic scattering of W bosons. We find that the unification scale is at about 10^{14} GeV. Viable grand unified theories must thus conserve baryon number. We discuss how to build such a model without using Higgs bosons.Comment: 8 pages, to be published in the proceedings devoted to the Scientific and Human Legacy of Julius Wess, initiated by the JW2011 Workshop, August 27 - 28, 2011, Donji Milanovac, Serbi

Soft versus Hard X-ray emission in AGN: partial covering and warm plus cold absorber models

We analyse the ROSAT PSPC hardness ratio and the 0.5-2 keV to 2-10 keV flux ratio of 65 Active Galactic Nuclei (AGN) for which there are both ROSAT archival observations available and 2-10 keV fluxes, mostly from the HEAO-1 MC-LASS survey. We conclude that the simplest spectral model for the AGN that can accommodate the variety of X-ray colours obtained is a standard power law (with energy spectral index $\alpha\sim 0.9$) plus a $\sim 0.1$ keV black body both partially absorbed. In our sample, type 1 AGN require an absorbing column around $10^{22}\, {\rm cm}^{-2}$ with covering fractions between 20 and 100\%, while type 2 AGN display larger columns and $\sim 100\%$ coverage. This simple model also provides a good link between soft and hard AGN X-ray luminosity functions and source counts. We also consider a warm absorber as an alternative model to partial covering and find that the the presence of gas in two phases (ionized and neutral) is required.Comment: 10 pages, Latex (mn.sty), 1 table, 5 figures included (epsf), postscript version also available via anonymous ftp at ftp://astsun1.unican.es/pub/ceballos/ . Accepted for publication in MNRA

Theoretical view on the origin and implications of structural distortions in polyoxometalates

Structural features of polyoxometalates (POMs) —versatile inorganic clusters of academic and technological interest— are discussed in the present article. POMs are, in general, very regular structures presenting a high symmetry in most cases. Distortions are, however, important for some electronic and magnetic properties. We herein discuss some particular geometric features that are crucial for the theoretical treatment and comprehension of well-known experimental phenomena. For instance, we have been able to understand and rationalize the geometrical distortions present in molybdenum POMs. Moreover, we can affirm that these geometrical distortions are caused by a pseudo Jahn Teller effect. In what concerns NMR chemical shifts, we present a discussion on the importance of geometry for the correct description of the signals and the key role played by the interatomic distances. Finally, a study on the adsorption of Keggin clusters on silver surfaces shows how the POM structure looses its regular shape to adapt to that new situation

Building self-evaluation skills through criterion-referenced assessment in public relations

Although technical skills in public relations are essential to practice, skills in self-evaluation, critical thinking, and problem solving are required when new practitioners move to management roles (Van Leuven, 1999). Public relations courses integrate specialist subject knowledge with graduate skill sets and capabilities in non-technical areas (Butcher & Stefani, 1995). Given that autonomy in learning is a skill valued by employers (Clifford, 1999) and advocated by accrediting professional bodies (Anderson, 1999), this study explores how public relations students build skills in and perceive the practice of self-evaluation. Currently, the public relations education literature presents a limited treatment of self-evaluation. Therefore, this study is guided mostly by the education literature and uses criterion-referenced assessment to determine how more than 150 students understand assessment requirements, assess their strengths and weaknesses, and interpret the differences between their self and their tutor's judgement of performance. The results indicate strong support for student understanding of assessment requirements and self-evaluation techniques but lower than expected support for understanding the differences between their self and tutor judgements. These findings are significant to educators, practitioners and professional bodies as they have implications for lifelong learning for public relations professionals