173 research outputs found
Personalizing and Improving Resource Recommendation by Analyzing Users Preferences in Social Tagging Activities
Collaborative tagging which is the keystone of the social practices of web 2.0 has been highly developed in the last few years. In this paper, we propose a new method to analyze user profiles according to their tagging activity in order to improve resource recommendation. We base upon association rules which is a powerful method to discover interesting relationships among large datasets on the web. Focusing on association rules we can find correlations between tags in a social network. Our aim is to recommend resources annotated with tags suggested by association rules, in order to enrich user profiles. The effectiveness of the recommendation depends on the resolution of social tagging drawbacks. In our recommender process, we demonstrate how we can reduce tag ambiguity and spelling variations problems by taking into account social similarities calculated on folksonomies, in order to personalize resource recommendation. We surmount also the lack of semantic links between tags during the recommendation process. Experiments are carried out with two different scenarios: the first one is a proof of concept over two baseline datasets and the second one is a real world application for diabetes disease
THERMAL, PHOTONIC AND MAGNETIC STUDIES OF THIAZYL RADICALS
Chapter 1 provides an overview of the area of 1,2,3,5-dithiadiazolyl (DTDA) radical chemistry which is central to this thesis, including a review of the crystal engineering principles and the physical properties of DTDA radicals, focusing on structure-property relationships. The magnetic properties of the -polymorph of p-NCC6F4CNSSN have been almost exhaustively studied since 1993 when it was found to exhibit the highest magnetic ordering temperature (TN = 36 K) for an organic magnet. Conversely the structure and physical properties of the -polymorph have barely been explored. The conditions for the selective preparation of and polymorphs of this radical are investigated in Chapter 2. The relative polymorph stability is probed through detailed DSC and PXRD studies and the magnetic properties of the -polymorph fully examined through dc and ac susceptibility measurements coupled with heat capacity studies. In Chapters 3 and 4, systematic structural studies on the variation of substituent groups are undertaken, comprising a series of alkoxy-functionalised perfluorophenyl DTDA radicals, p-ROC6F4CNSSN (R = Me, Et, Pr, Bu) and a comparison of the substitution pattern of the tolyl group on PhDTDA derivatives, MeC6H4C6H4CNSSN and their polymorphs. These studies use a combination of single crystal and VT-PXRD, SQUID magnetometry and VT EPR spectroscopy combined with DSC measurements and computational studies to probe relative polymorph stabilities and magnetic properties. A new generation of DTDA radicals where the R substituent is “non-innocent” are described in Chapters 5 and 6. In Chapter 5 the synthesis and characterisation of a series of DTDA-functionalised polyaromatic hydrocarbons (PAH) are described and their polymorphism examined as well as their solution and solid state optical properties. These reveal fluorescence quantum efficiencies up to 50%. Radical stability can be enhanced through incorporation into polymer matrices (PMMA and PS) which retard hydrolysis and prototype OLEDs based on a fluorescent DTDA exhibiting a luminance of almost 2000 Cd/m2 is described. Chapter 6 describes two stilbene-based DTDA diradicals in which the potential for thermal and photochemical cis/trans isomerisation, ring closure or [2+2] cycloaddition was explored. Solution photochemistry reactions, monitored by 1H NMR, UV/vis and fluorescence studies and EPR spectroscopy) revealed a trans/cis isomerisation, followed by ring-closure to afford a dihydrophenanthrene intermediate which undergoes H-atom migration with quenching of radical paramagnetism. Subsequent thermal treatment affords a phenanthrene-based diradical species with an increase in sample paramagnetism. Chapter 7 provides a brief overview of the results obtained in this thesis, the insight that these results provide within this research area and the potential for future exploitation
Application of Current Algebra in Three Pseudoscalar Meson Decays of Lepton
The decays of and
are calculated using the hard pion and kaon current algebra and assuming the
Axial-Vector meson dominance of the hadronic axial currents. Using the
experimental data on their masses and widths, the decay branching ratios
into these channels are calculated and found to be in a reasonable agreement
with the experimental data. In particular, using the available Aleph data on
the spectrum, we determine the parameters, ,
GeV; the hard current algebra calculation yields a
branching ratio of .Comment: 14 pages, Tex, 6 included figure
Schedule for CT image guidance in treating prostate cancer with helical tomotherapy.
The aim of this study was to determine the effect of reducing the number of image guidance sessions and patient-specific target margins on the dose distribution in the treatment of prostate cancer with helical tomotherapy. 20 patients with prostate cancer who were treated with helical tomotherapy using daily megavoltage CT (MVCT) imaging before treatment served as the study population. The average geometric shifts applied for set-up corrections, as a result of co-registration of MVCT and planning kilovoltage CT studies over an increasing number of image guidance sessions, were determined. Simulation of the consequences of various imaging scenarios on the dose distribution was performed for two patients with different patterns of interfraction changes in anatomy. Our analysis of the daily set-up correction shifts for 20 prostate cancer patients suggests that the use of four fractions would result in a population average shift that was within 1 mm of the average obtained from the data accumulated over all daily MVCT sessions. Simulation of a scenario in which imaging sessions are performed at a reduced frequency and the planning target volume margin is adapted provided significantly better sparing of organs at risk, with acceptable reproducibility of dose delivery to the clinical target volume. Our results indicate that four MVCT sessions on helical tomotherapy are sufficient to provide information for the creation of personalised target margins and the establishment of the new reference position that accounts for the systematic error. This simplified approach reduces overall treatment session time and decreases the imaging dose to the patient
Dispersive representation of the scalar and vector Kpi form factors for tau --> K pi nu_tau and K_{l3} decays
Recently, the tau --> K pi nu_tau decay spectrum has been measured by the
Belle and BaBar collaborations. In this work, we present an analysis of such
decays introducing a dispersive parametrization for the vector and scalar Kpi
form factors. This allows for precise tests of the Standard Model. For
instance, the determination of f_+(0)|V_{us}| from these decays is discussed. A
comparison and a combination of these results with the analyses of the K_{l3}
decays is also considered.Comment: 6 pages, 1 figure. Talk given at 11th International Workshop on Tau
Lepton Physics, Manchester, UK, 13-17 September 201
Decay and Scattering
Using chiral low energy theorems and elastic unitarity assumption, the
decay is investigated. The vector and scalar form
factors are calculated. It is found that the spectrum is dominated by
the resonance. By measuring the forward-backward asymmetry, it is shown
that the S wave phase shift can be determined near the
resonance region. The calculated branching ratio and resonance parameters are
in good agreement with experiments.Comment: 15 pages, Tex, 6 included figure
Pion-Kaon Scattering near the Threshold in Chiral SU(2) Perturbation Theory
In the context of chiral SU(2) perturbation theory, pion-kaon scattering is
analysed near the threshold to fourth chiral order. The scattering amplitude is
calculated both in the relativistic framework and by using an approach similar
to heavy baryon chiral perturbation theory. Both methods lead to equivalent
results. We obtain relations between threshold parameters, valid to fourth
chiral order, where all those combinations of low-energy constants which are
not associated with chiral-symmetry breaking terms drop out. The remaining
low-energy constants can be estimated using chiral SU(3) symmetry.
Unfortunately, the experimental information is not precise enough to test our
low-energy theorems.Comment: 38 pages, 5 figures, PhD Thesis, references adde
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