1,721,049 research outputs found
Effects and phenomenology of cut-off physics on the primordial universe
Full text linkThe main focus of this thesis is the implementation of alternative quantization procedures, developed to easily introduce quantum gravitational corrections, on cosmological models. The aim is to study the fate of cosmological singularities and to derive possible signatures of more fundamental Quantum Gravity theories.
Polymer Quantum Mechanics (PQM) is a procedure of quantization on a lattice, inspired by Loop Quantum Gravity but derived independently. The discretization of a position-like variable implies a cut-off on the corresponding momentum, and its implementation on the cosmological minisuperspaces, called Polymer Cosmology, is usually able to remove the Big Bang and Big Crunch singularities, replacing them with a Big Bounce similarly to Loop Quantum Cosmology. However the properties of the Bounce, i.e. its universality or its dependence on initial conditions, depend on the geometrical nature of the variable chosen to describe the model. After a comparison of different sets of variables in the isotropic Friedmann-Lema\^itre-Robertson-Walker model, the privileged variable to obtain a universal Bounce is identified in the cubed scale factor corresponding to the comoving volume. The recovery of the equivalence between different sets of variables after the discretization has been implemented is still an open question, and it can have implications for Loop Quantum Cosmology.
The Generalized Uncertainty Principle representation (GUP), inspired by String Theories, introduces higher-order corrections on the canonical commutation relations and implies an absolute minimal uncertainty on position. Its cosmological implementation however is not usually able to remove the singularities; furthermore, the recreation of Brane Cosmology (a cosmological sector of String Theories) happens only for a different variation of this representation. Indeed, it is possible to extend the GUP formulation to different functions of the momentum, obtaining deformed commutation relations known as Modified Algebras. Not all of them imply minimal uncertainties, but some can introduce energy cut-offs. In particular, there are specific formulations able to reproduce Polymer Cosmology and Brane Cosmology. Another interesting form is able to remove singularities not through a Bounce but through an asymptotic behaviour; this way it is possible to reproduce the so-called Emergent Universe model without the fine tuning needed on a classical level.
Modified Algebras can be used to easily derive corrections to the primordial Power Spectrum of scalar perturbations, thus yielding a possibly observable signature of quantum gravitational corrections. When applied to the gravitational collapse of a dust cloud, they are able to halt the collapse and prevent the formation of Black Holes, thus possibly explaining the recently observed violations of star mass limits.
This thesis represents a starting point for the development of alternative quantization procedures as a somewhat phenomenological approach to implement corrections from more fundamental Quantum Gravity theories. There is still the need to define and develop canonical transformations between different sets of variables, since at the moment they seem to yield inequivalent dynamics; furthermore, the algebras can have different operatorial representations whose equivalence must still be formally proven. Finally, their implementation on more complex systems such as the anisotropic and chaotic Bianchi IX model or inhomogeneous solutions could be useful towards the further development of a complete theory of Quantum Gravity
Volatile chlorinated hydrocarbons in Antarctica. Analytical aspects and environmental evaluation
No full textDetermination of Endogenous and Synthetic Glucocorticoids in Human Urine by Gas Chromatography – Mass Spectrometry Following Microwave Assisted Derivatization
Full text linkAcomplete screening and confirmation analytical method for the direct determination of six endogenous (cortisol, cortisone, deoxycorticosterone, tetrahydrocortisol, tetrahydrocortisone, tetrahydro-S) and 17 synthetic (amcinonide, betamethasone, desoximethasone, dexamethasone, fludrocortisone, flumethasone, flunisolide, flucinolone acetonide, flucinonide, fluprednisolone, flurandrenolide, fluorometholone, 6-methylprednisolone, prednisolone, prednisone, triamcinolone, triamcinolone acetonide) glucocorticoids in human urine by gas chromatography with mass spectrometric detection (GC–MS) is presented. The analytical technique comprises a pre treatment procedure and the instrumental analysis of the trimethylsilyl (TMS) derivatives, performed by GC–MS (quadrupole) with electron impact (EI) ionization. The derivatization yields obtained by two different derivatizing mixtures, namely N-methyl N(trimethylsilyl)trifluoroacetamide (MTSFA):NH4I:dithioerythritol (DTE) 1000:2:4 (usually indicated as TMSiodine); and N-trimethylsilylimidazole (TMSim):N,O-bis(trimethylsilyl)acetamide (BSA):trimethylchlorosilane (TMCS) 3:3:2, both under direct thermal heating and with microwave (MW) irradiation, were evaluated, also as a function of the temperature, of the MWì power and of the incubation time. The highest yields of the derivatization process were obtained, for most of the compounds here considered, by a two-step procedure: a microwave-assisted derivatization stage (40 min in a microwave oven at 900Wemitted power), followed by a traditional heat transfer derivatization (1.5 h in a thermostated bath at 70 ◦C) with the derivatization mixture TMSim:BSA:TMCS 3:3:2. In these operating conditions, diagnostic EI–MS spectra of all considered glucocorticoids were obtained. Limits of detection (LOD) of synthetic glucocorticoids in urine ranged from 3 to 25g/l. The effectiveness of the method for the determination of glucocorticoids in urine was evaluated on spiked urine samples and on real samples obtained from patients
under pharmacological treatment with synthetic glucocorticoids. Apart from the clinical monitoring of glucocorticoids in urine, the method can be applied as a complete screening + confirmation analytical protocol in antidoping tests for the detection of illicit administration of glucocorticoids by the athletes
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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