233 research outputs found
Joining Spacetimes on Fractal Hypersurfaces
The theory of fractional calculus is attracting a lot of attention from
mathematicians as well as physicists. The fractional generalisation of the
well-known ordinary calculus is being used extensively in many fields,
particularly in understanding stochastic process and fractal dynamics. In this
paper, we apply the techniques of fractional calculus to study some specific
modifications of the geometry of submanifolds. Our generalisation is applied to
extend the Israel formalism which is used to glue together two spacetimes
across a timelike, spacelike or a null hypersurface. In this context, we show
that the fractional extrapolation leads to some striking new results. More
precisely we demonstrate that, in contrast to the original Israel formalism,
where many spacetimes can only be joined together through an intermediate thin
hypersurface of matter satisfying some non- standard energy conditions, the
fractional generalisation allows these spacetimes to be smoothly sewed together
without any such requirements on the stress tensor of the matter fields. We
discuss the ramifications of these results for spacetime structure and the
possible implications for gravitational physics.Comment: 22 pages, 2 figure
Automatic Generation of Personalized Recommendations in eCoaching
Denne avhandlingen omhandler eCoaching for personlig livsstilsstøtte i sanntid ved bruk av informasjons- og kommunikasjonsteknologi. Utfordringen er å designe, utvikle og teknisk evaluere en prototyp av en intelligent eCoach som automatisk genererer personlige og evidensbaserte anbefalinger til en bedre livsstil. Den utviklede løsningen er fokusert på forbedring av fysisk aktivitet. Prototypen bruker bærbare medisinske aktivitetssensorer. De innsamlede data blir semantisk representert og kunstig intelligente algoritmer genererer automatisk meningsfulle, personlige og kontekstbaserte anbefalinger for mindre stillesittende tid. Oppgaven bruker den veletablerte designvitenskapelige forskningsmetodikken for å utvikle teoretiske grunnlag og praktiske implementeringer. Samlet sett fokuserer denne forskningen på teknologisk verifisering snarere enn klinisk evaluering.publishedVersio
Kalb-Ramond field interactions in a braneworld scenario
Electromagnetic and (linearized) gravitational interactions of the
Kalb-Ramond (KR) field, derived from an underlying ten dimensional heterotic
string in the zero slope limit, are studied in a five dimensional background
Randall-Sundrum I spacetime with standard model fields confined to the visible
brane having negative tension. The warp factor responsible for generating the
gauge hierarchy in the Higgs sector is seen to appear inverted in the KR field
couplings, when reduced to four dimensions. This leads to dramatically enhanced
rotation, {\it far beyond observational bounds}, of the polarization plane of
electromagnetic and gravitational waves, when scattered by a homogeneous KR
background. Possible reasons for the conflict between theory and observation
are discussed.Comment: 13 pages Latex, no figures, discussion and acknowledgements adde
Hawking radiation from dynamical horizons
In completely local settings, we establish that a dynamically evolving black
hole horizon can be assigned a Hawking temperature. Moreover, we calculate the
Hawking flux and show that the radius of the horizon shrinks.Comment: 5 Page
Personalized Recommendations for Physical Activity e-Coaching (OntoRecoModel): Ontological Modeling
publishedVersio
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