1,790 research outputs found
On the groundstate energy of tight knots
New results on the groundstate energy of tight, magnetic knots are presented.
Magnetic knots are defined as tubular embeddings of the magnetic field in an
ideal, perfectly conducting, incompressible fluid. An orthogonal, curvilinear
coordinate system is introduced and the magnetic energy is determined by the
poloidal and toroidal components of the magnetic field. Standard minimization
of the magnetic energy is carried out under the usual assumptions of volume-
and flux-preserving flow, with the additional constraints that the tube
cross-section remains circular and that the knot length (ropelength) is
independent from internal field twist (framing). Under these constraints the
minimum energy is determined analytically by a new, exact expression, function
of ropelength and framing. Groundstate energy levels of tight knots are
determined from ropelength data obtained by the SONO tightening algorithm
developed by Pieranski (Pieranski, 1998) and collaborators. Results for torus
knots are compared with previous work done by Chui & Moffatt (1995), and the
groundstate energy spectrum of the first prime knots (up to 10 crossings) is
presented and analyzed in detail. These results demonstrate that ropelength and
framing determine the spectrum of magnetic knots in tight configuration.Comment: 26 pages, 9 figure
The European ex situ PGR Information Landscape
In this paper the authors try to describe the current situation regarding the documentation of Plant Genetic Resources (PGR) maintained in ex situ collections in Europe. It will tackle the systems that are used to manage the information involved, the mechanisms and systems that exist to exchange this information, and we will discuss the developments and challenges in this area. Apart from this technical description, the authors also try to give a functional description of the changing role of these systems in the light of international, technical and legal developments
The construction and evaluation of a test of ability to read and interpret graphs for grades six, seven and eight.
Thesis (Ed.M.)--Boston Universit
Domestication, diversity and use of Brassica oleracea L., based on ancient Greek and Latin texts
The domestication process of Brassica oleracea L. has not been fully clarified, either regarding its initial location or the progenitor species involved. Two alternative hypotheses proposed so far point to either a northwest European or a Mediterranean location. Previous studies to clarify the domestication process focused on linguistic aspects and on the earliest occurrences in ancient literature of words referring to B. oleracea. Those studies are here extended to offer a comprehensive account of literary occurrences of the brassica vegetables in ancient Greek and Latin texts, between the VI century B.C.E. and the IV century C.E. This study offers a contribution to ancient ethnobotanical knowledge in the Mediterranean, including agricultural practices and culinary and medicinal uses. It also defines the time when increasing diversity of crop varieties is documented and it adds weight to the hypothesis of a Mediterranean location of the domestication of B. oleracea
Velocity, energy and helicity of vortex knots and unknots
In this paper we determine the velocity, the energy and estimate writhe and
twist helicity contributions of vortex filaments in the shape of torus knots
and unknots (toroidal and poloidal coils) in a perfect fluid. Calculations are
performed by numerical integration of the Biot-Savart law. Vortex complexity is
parametrized by the winding number , given by the ratio of the number of
meridian wraps to that of the longitudinal wraps. We find that for vortex
knots and toroidal coils move faster and carry more energy than a reference
vortex ring of same size and circulation, whereas for knots and poloidal
coils have approximately same speed and energy of the reference vortex ring.
Helicity is dominated by the writhe contribution. Finally, we confirm the
stabilizing effect of the Biot-Savart law for all knots and unknots tested,
that are found to be structurally stable over a distance of several diameters.
Our results also apply to quantized vortices in superfluid He.Comment: 17 pages, 8 figures, 2 table
Organic and healthy: assessing the impact of claims and third-party certifications on premium price
Organic food consumption is steadily growing across a variety of product categories. While consumers are increasingly focused on the healthiness of the food they purchase, companies are experimenting alternative ways to communicate and guarantee the organic and health-related benefits of their products. This study explores the effect of different combinations of front-of-package (FoP) components on premium price. Specifically, we focus on the interaction and visual salience of FoP organic claims, health-related claims, and third-party organic certifications. Based on an analysis of grocery sales data and product packaging visuals, the study identifies FoP component combinations that could maximise premiums. We offer insights to marketing managers and companies involved in enhancing the communication of organic food benefits to consumers
Minutes of a joint meeting of the documentation and information network coordinating group and the EURISCO Advisory Group: Planning for the continuation of EPGRIS, 2-3 April 2007, Rome, Italy
Smelling the Space Around Us: Odor Pleasantness Shifts Visuospatial Attention in Humans
The prompt recognition of pleasant and unpleasant odors is a crucial regulatory and adaptive need of humans. Reactive answers to unpleasant odors ensure survival in many threatening situations. Notably, although humans typically react to certain odors by modulating their distance from the olfactory source, the effect of odor pleasantness over the orienting of visuospatial attention is still unknown. To address this issue, we first trained participants to associate visual shapes with pleasant and unpleasant odors, and then we assessed the impact of this association on a visuospatial task. Results showed that the use of trained shapes as flankers modulates performance in a line bisection task. Specifically, it was found that the estimated midpoint was shifted away from the visual shape associated with the unpleasant odor, whereas it was moved toward the shape associated with the pleasant odor. This finding demonstrates that odor pleasantness selectively shifts human attention in the surrounding space
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