A Symmetry for the Cosmological Constant

We study a symmetry, schematically Energy -> - Energy, which suppresses matter contributions to the cosmological constant. The requisite negative energy fluctuations are identified with a "ghost" copy of the Standard Model. Gravity explicitly, but weakly, violates the symmetry, and naturalness requires General Relativity to break down at short distances with testable consequences. If this breakdown is accompanied by gravitational Lorentz-violation, the decay of flat spacetime by ghost production is acceptably slow. We show that inflation works in our scenario and can lead to the initial conditions required for standard Big Bang cosmology.Comment: 18 pages, 3 figures, References correcte

Lines, Circles, Planes and Spheres

Let $S$ be a set of $n$ points in $\mathbb{R}^3$, no three collinear and not all coplanar. If at most $n-k$ are coplanar and $n$ is sufficiently large, the total number of planes determined is at least $1 + k \binom{n-k}{2}-\binom{k}{2}(\frac{n-k}{2})$. For similar conditions and sufficiently large $n$, (inspired by the work of P. D. T. A. Elliott in \cite{Ell67}) we also show that the number of spheres determined by $n$ points is at least $1+\binom{n-1}{3}-t_3^{orchard}(n-1)$, and this bound is best possible under its hypothesis. (By $t_3^{orchard}(n)$, we are denoting the maximum number of three-point lines attainable by a configuration of $n$ points, no four collinear, in the plane, i.e., the classic Orchard Problem.) New lower bounds are also given for both lines and circles.Comment: 37 page

Channel diffusion of sodium in a silicate glass

We use classical molecular dynamics simulations to study the dynamics of sodium atoms in amorphous Na$_2$O-4SiO$_2$. We find that the sodium trajectories form a well connected network of pockets and channels. Inside these channels the motion of the atoms is not cooperative but rather given by independent thermally activated hops of individual atoms between the pockets. By determining the probability that an atom returns to a given starting site, we show that such events are not important for the dynamics of this system.Comment: 10 pages of Latex, 5 figures, one figure added, text expande

Higgs Scalars in the Minimal Non-minimal Supersymmetric Standard Model

We consider the simplest and most economic version among the proposed non-minimal supersymmetric models, in which the $\mu$-parameter is promoted to a singlet superfield, whose all self-couplings are absent from the renormalizable superpotential. Such a particularly simple form of the renormalizable superpotential may be enforced by discrete $R$-symmetries which are extended to the gravity-induced non-renormalizable operators as well. We show explicitly that within the supergravity-mediated supersymmetry-breaking scenario, the potentially dangerous divergent tadpoles associated with the presence of the gauge singlet first appear at loop levels higher than 5 and therefore do not destabilize the gauge hierarchy. The model provides a natural explanation for the origin of the $\mu$-term, without suffering from the visible axion or the cosmological domain-wall problem. Focusing on the Higgs sector of this minimal non-minimal supersymmetric standard model, we calculate its effective Higgs potential by integrating out the dominant quantum effects due to stop squarks. We then discuss the phenomenological implications of the Higgs scalars predicted by the theory for the present and future high-energy colliders. In particular, we find that our new minimal non-minimal supersymmetric model can naturally accommodate a relatively light charged Higgs boson, with a mass close to the present experimental lower bound.Comment: 63 pages (12 figures), extended versio

Is symmetry identity?

Wigner found unreasonable the "effectiveness of mathematics in the natural sciences". But if the mathematics we use to describe nature is simply a coded expression of our experience then its effectiveness is quite reasonable. Its effectiveness is built into its design. We consider group theory, the logic of symmetry. We examine the premise that symmetry is identity; that group theory encodes our experience of identification. To decide whether group theory describes the world in such an elemental way we catalogue the detailed correspondence between elements of the physical world and elements of the formalism. Providing an unequivocal match between concept and mathematical statement completes the case. It makes effectiveness appear reasonable. The case that symmetry is identity is a strong one but it is not complete. The further validation required suggests that unexpected entities might be describable by the irreducible representations of group theory

The geology and geophysics of Kuiper Belt object (486958) Arrokoth

The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, are primitive objects preserving information about Solar System formation. The New Horizons spacecraft flew past one of these objects, the 36 km long contact binary (486958) Arrokoth (2014 MU69), in January 2019. Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters diameter) within a radius of 8000 km, and has a lightly-cratered smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism

Articulating choice and deliberation in conducting research - researchers 'working in the interpretive zone'.

Gedragsveranderingen bij leerlingen en hun lerare

The semiology of changing brand image

This article considers the attempted change to the image of an established brand by studying the semiotics within the brand’s historical advertising campaigns. The use of semiotics to study the interpretation of messages is discussed, and the link between interpretation of messages and advertising effectiveness in changing brand image is explored. The authors deconstruct advertisements of a brand to provide a model containing opposing dialectics that may aid managers by highlighting alternative symbolic messages contained in advertisements. Oncwe identified, these alternative symbolic messages may be used to help change brand image and influence advertising effectiveness. Although the study focuses upon a major brand of beer, this is an industry in which there are numerous small firms, and many of those have constrained marketing budgets, and thus need to make sure that their advertising is effective. Equally, entrepreneurial marketing is not to found only in the small firm, and the case study discusses a radical and imaginative brand repositioning of a well established product

Comparison of Physical-chemical and Mechanical Properties of Chlorapatite and Hydroxyapatite Plasma Sprayed Coatings

Chlorapatite can be considered a potential biomaterial for orthopaedic applications. Its use as plasma-sprayed coating could be of interest considering its thermal properties and particularly its ability to melt without decomposition unlike hydroxyapatite. Chlorapatite (ClA) was synthesized by a high-temperature ion exchange reaction starting from commercial stoichiometric hydroxyapatites (HA). The ClA powder showed similar characteristics as the original industrial HA powder, and was obtained in the monoclinic form. The HA and ClA powders were plasma-sprayed using a low-energy plasma spraying system with identical processing parameters. The coatings were characterized by physical-chemical methods, i.e. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy, including distribution mapping of the main phases detected such as amorphous calcium phosphate (ACP), oxyapatite (OA), and HA or ClA. The unexpected formation of oxyapatite in ClA coatings was assigned to a side reaction with contaminating oxygenated species (O2, H2O). ClA coatings exhibited characteristics different from HA, showing a lower content of oxyapatite and amorphous phase. Although their adhesion strength was found to be lower than that of HA coatings, their application could be an interesting alternative, offering, in particular, a larger range of spraying conditions without formation of massive impurities.This study was carried out under a MNT ERA-Net Project named NANOMED. The authors gratefully thank the Midi-Pyrénées region (MNT ERA Net Midi-Pyrénées Région, NANOMED2 project) and the Institute National Polytechnique de Toulouse (BQR INPT 2011, BIOREVE project) for supporting this research work, especially the financial support for research carried out in the CIRIMAT and the LGP laboratories (France), and the Basque government and Tratamientos Superficiales Iontech, S.A. for their financial and technical support under the IG-2007/0000381 grant for the development of the LEPS device and deposition of the coatings carried out in Inasmet-Tecnalia. The French industrial collaborators (TEKNIMED SA and 2PS SA) were financed by the OSEO programs