1,721,003 research outputs found
Quantum gravity corrections to quantum field theory: Born-Oppenheimer approach to the canonical formalism
Full text linkThe role of time is intrinsically different between Quantum Mechanics and General Relativity: while the former associates time with an external observer, the latter unifies time and space, making them indistinguishable in a covariant framework. The absence of a clear time variable in GR stems from its symmetry and parametrized nature, resulting in the so-called frozen formalism.
For this reason, the search for a theory of Quantum Gravity must face the challenge of time absence in the Wheeler-de Witt equation.
Efforts to quantize gravity have led to various approaches to define time, categorized into pre-quantization, post-quantization, and timeless proposals. This thesis focuses on post-quantization time constructions, particularly within the Wentzel-Kramers-Brillouin approach, which perturbatively expands the wave function to derive dynamical equations. Previous attempts have shown that the introduction of an internal clock from gravitational variables yields non-unitary dynamical effects on the matter sector at the next order.
This thesis implements a Born-Oppenheimer-like scheme that separates the matter and gravitational sectors, leveraging their distinct energy scales: the matter's faster evolution is contrasted with the slower gravitational field, both properly quantum.
Two novel time constructions are proposed, making use of a fast component derived from introducing the kinematical action or (reparametrized) Gaussian frame fixing respectively; the discussion of their geometrical and physical meaning proves that both are essentially tied to the concept of a reference system.
These clocks for the matter subsystem overcome previous non-unitarity concerns, resulting in an Hermitian dynamics at the first order where quantum-gravitational corrections emerge. A direct equivalence between the two implementations is proved in the homogeneous minisuperspace setting.
The present investigation also faces the challenge posed by the dependence of the matter wave functional on intrinsically quantum gravitational components, particularly evident in the cosmological context. To address this, a more rigorous Born-Oppenheimer separation of dynamics is proposed, distinguishing the classical gravitational background from its small quantum fluctuations (i.e. gravitons) and then proper quantum matter contributions. By introducing an appropriate gauge choice for the gravitons' sector, the zero-th order of this model allows to recover the standard Quantum Field Theory dynamics.
We show how this refined scheme can be combined with the concept of a reference fluid time (or equivalently the kinematical action one), offering a unitary evolution for the quantum matter subsystem with quantum gravity corrections, free of previously mentioned concerns.
Such unified approach clarifies the quantum nature of gravitational components and shows how gauge requirements address the emergence of quantum gravity effects in subsequent orders of the expansion.
The central achievement of the present thesis is the development of a suitable Born-Oppenheimer scheme for the quantum gravity-matter system, in which the matter's evolution modified by quantum gravitational effects has a unitary character. This framework offers insights into how quantum gravity influences our understanding of the universe and contributes to a deeper comprehension of gravitational phenomena
Leptin receptor identification in canine skin
No full textLeptin is a polypeptide secreted by adipose tissue regulating
appetite and energy consumption. It acts by binding with a specific
receptor that is expressed in various tissues suggesting that
leptin might exert diverse biological functions other than energy
metabolism. Accordingly, leptin acts as a mitogen for a growing
number of cell types, including the epidermis where it was detected
together with its receptor. In particular, leptin strongly stimulate
a proliferative response of keratinocytes during skin repair. Moreover,
leptin and its receptor were detected in hair follicle where
it may be involved in the control of hair follicle morphogenesis.
At present, this hormone is considered a novel therapeutic factor
to improve severely disturbed wound-healing conditions. To evaluate
the action of leptin in the skin of the dog, we investigated
the presence and localization of leptin receptor by using immunohistochemical
technique. Through the application of a polyclonal
antibody, we observed the expression of the receptor in the cells of
the basal layer of the epidermis, in the hair follicles and in the apical
membrane of the apocrine sweat gland cells. As regards hair follicles,
the positivity was observed in the cells of the outer root sheath both in growing and regressive phase. The identification of leptin
receptor suggests an important role of leptin in the metabolism of
the epidermis and skin structures in canine species
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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