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Search Results: 1 - 10 of 6560 matches for " Alex Venditti "
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Considerations of particle definitions in the functional Schroedinger formalism
Alex Venditti,Charles Dyer
Physics , 2011,
Abstract: It is often remarked in the literature that particles in QFT on curved spacetime are akin to coordinates in general relativity and hence are physically meaningless. This moral is given an explicit demonstration by giving the correspondence between the coordinates on phase space for a field theory and the particle number. Usually the ambiguity in particle definitions is only as varied as the possible sets of observers on the spacetime. However, there is a greater choice in coordinates on the phase space, especially for a field system with infinite degrees of freedom. Hence, for one set of coordinates on the spacetime (one class of comoving observers) there are many different coordinates to choose on the phase space. This demonstrates the true vacuousness of the concept of particles when defined as energy levels of the harmonic oscillator. In order to give a definition of particles we must specify the apparatus that detects them. The Unruh-Dewitt detector is one such apparatus, so we are not surprised to find that it gives a physically meaningful definition of particles. We give an explicit example on de Sitter spacetime and explain how the definition of particles as energy levels of the harmonic oscillator is meaningless even in simple cases. This is done first by comparing the response of an Unruh-Dewitt detector to the expectation of the number operator. Second, we demonstrate that by a choice of coordinates on phase space one can turn the Hamiltonian of a free Klein-Gordon field on FRW with flat spatial sections into a set of harmonic oscillators with time-independent mass and frequency. Also, we demonstrate a new method for determining the wave functional of known states such as the conformal vacuum.
The Casimir effect in a topologically closed Minkowski spacetime
Alex Venditti,Charles Dyer
Physics , 2013,
Abstract: Results concerning the Casimir effect in a topologically closed Minkowski spacetime.
On the Response of Particle Detectors in Vaidya Spacetimes
Alex Venditti,Charles Dyer
Physics , 2012, DOI: 10.1088/0264-9381/30/6/065004
Abstract: Using the formalism of the interaction picture we calculate an expression for the Wightman function for only the spherically symmetric modes of a quantum Klein-Gordon scalar field in a general Vaidya spacetime with ingoing null dust. It is demonstrated that particle detectors following time-like trajectories that are in the ground state at some time outside of the collapsing shell will respond independently from the configuration of the ingoing null dust if the response is taken at any time outside of the collapsing shell. For detectors that are taken to be in the ground state at a time interior to the shell it is shown that their response will depend on the configuration of the ingoing null dust. Relevance to the information loss paradox is discussed.
Choosing a vacuum state in a spherical spacetime with a conformal Killing vector
Alex Venditti,Charles Dyer
Physics , 2012,
Abstract: We consider the problem of picking a physically motivated vacuum state on a spherically symmetric spacetime with an extra conformal Killing vector, as opposed to an extra Killing vector as in the Schwarzschild case. Considering a conformal symmetry instead of a symmetry allows us to consider spacetimes that are dynamical and not static (like Schwarzschild). The extra conformal symmetry allows us to calculate the response of particle detectors however. We look at the specific example of a self-similar LTB spacetime that represents a spherically symmetric but inhomogeneous cosmology. We remark that the above procedure might be applied to a spherically symmetric collapse solution that represents black hole formation so that one can calculate the detailed spectrum of Hawking radiation during a collapse.
Self-reported cigarette smoking status imprecisely quantifies exposure in pregnancy  [PDF]
Carolina C. Venditti, Graeme N. Smith
Open Journal of Obstetrics and Gynecology (OJOG) , 2012, DOI: 10.4236/ojog.2012.21010
Abstract: Objective: We sought to determine the validity of self-reported smoking activity versus two quantitative measurements of tobacco exposure in pregnancy. We hypothesized that pregnant women would under-report their daily smoking amounts, due to the negative social stigmas associated with such a behavior. Methods: Cigarette-smoking and non-smoking pregnant women were recruited as part of a larger research study. Pregnant women with a singleton baby (>24 weeks) were recruited at a clinical appointment or prior to an elective caesarian section. Self-reported smoking status, including time since last cigarette, was recorded. End-tidal breath carbon monoxide (ETCO) levels and urine cotinine levels were measured and compared. Results: Both normotensive non-smoking (NTN) (n = 44) and normotensive smoking (NTS) (n = 24) pregnant women were recruited. A strong correlation was found between ETCO levels and urine cotinine measurements (r = 0.6566, p < 0.05). Self-reported smoking status in NTS was poorly correlated with ETCO levels (r = 0.5356, p < 0.05) and urine cotinine levels (r = 0.0324, P > 0.05). Conclusion: Self-reported smoking status accurately identifies women who smoke in pregnancy, but not their level of tobacco exposure. Urine cotinine or ETCO are much better quantitative measurements of nicotine and carbon monoxide, respectively, and should be measured for a more precise indicator of smoking activity. These devices will allow for better counseling and monitoring of women who are trying to quit smoking and/or who enter into smoking cessation programs.
High- and Low-Rearing Rats Differ in the Brain Excitability Controlled by the Allosteric Benzodiazepine Site in the GABAA Receptor  [PDF]
Rosana Alves, José Gilberto Barbosa de Carvalho, Marco Antonio Campana Venditti
Journal of Behavioral and Brain Science (JBBS) , 2012, DOI: 10.4236/jbbs.2012.23036
Abstract: Rearing is an exploratory behavior induced by novelty, such as exposure to an open field. Stimulation of certain brain regions, including the hippocampus, induces both rearing and clonic convulsions. Brain excitability is controlled by gamma-aminobutyric acid (GABA) inhibitory neurotransmission through its ionotropic GABAA/allosteric benzodiazepine site. Drugs that decrease GABAA receptor fast inhibitory neurotransmission induce clonic convulsions and rearing when injected into the hippocampus. Therefore, individual differences in rearing behavior may be related to the susceptibility to clonic convulsions, which could involve differences in brain excitability controlled by GABAA/allosteric benzodiazepine site receptors. Adult, male Wistar rats were divided into high- (HR) and low-rearing (LR) groups based on the number of rearings in the open field test. Groups of HR and LR rats were challenged with convulsant drugs that antagonize GABA neurotransmission via different mechanisms of action (3-mercaptopropionic acid, a glutamate decarboxilase inhibitor; bicuculline, a GABAA receptor antagonist; pentylenetetrazol and picrotoxin, both GABAA receptor chloride channel blockers and DMCM, a benzodiazepine inverse agonist). The convulsant doses that induced 50% of clonic convulsions were determined for each drug. The LR rats had a higher susceptibility (a lower convulsant dose 50%) to clonic convulsions induced by DMCM than the HR rats, but there were no differences between the groups in the susceptibility to tonic convulsions induced by the same drug. There were no significant differences in the convulsant dose 50% for clonic convulsions between the groups for all other drugs injected. In another experiment, additional HR and LR rats were injected with a sedative-hypnotic dose of diazepam, which caused a significantly higher hypnotic effect (sleeping-time) in the LR rats than in the HR rats. The LR group was also shown to have a significantly lower density of [3H]-Flunitrazepam bound to the GABAA receptor in hippocampal membranes. Our data suggest that inter-individual differences in rearing are related, at least in part, to the GABA inhibitory neurotransmission controlled by the benzodiazepine allosteric site in the GABAA receptor.
Tornando o "Jogo Possível": Reflex es sobre a Pedagogia do Esporte, os fundamentos dos jogos desportivos coletivos e a aprendizagem Making the “Possible Game”: Reflections on Sport Pedagogy, Fundamentals of Team Sports and Sport Learning Haciendo el "juego posible": reflexiones sobre la Pedagogía del deporte, los fundamentos de los juegos deportivos colectivos y el aprender deportivo
Rubens Venditti Jr,Marlus Alexandre Sousa
Pensar a Prática , 2008, DOI: 19806183/rpp.v11i1.1796
Abstract: Este trabalho surge da necessidade de discuss es sobre o papel educacional do profissional de educa o física na aprendizagem esportiva e Pedagogia do Esporte. Relacionamos correntes teóricas da Pedagogia do Esporte com o ensino dos jogos desportivos coletivos. Para tanto, utilizamos como instrumento o jogo, ferramenta fundamental de ensino e oportunidade social, através de suas características lúdicas. O jogo pode contribuir para o desenvolvimento de valores éticos, sociais e morais, assim como para a constru o de metáforas que estabele am rela es entre o esporte e a vida, fazendo uso da ludicidade e do ensino reflexivo. Ambos fundamentam nosso embasamento teórico para a atua o em Pedagogia do Esporte, trazendo mais oportunidades, op es de escolha e reflex es sobre nossa atua o profissional. This research work derives from the need to discuss the educational role of the physical education professional in sport learning and sport pedagogy. We have related sport pedagogy theories with the teaching of team sports. We have used the game as an instrument which is a fundamental teaching tool as well as a social opportunity, through its playful characteristics. Games can contribute to the development of ethical, social, and moral values, and to the building of metaphors that can establish relations between sport and life, making use of playfulness and reflexive teaching. Both concepts are fundamental to our theoretical foundation and bring more opportunities, choice, and reflections to our professional work. Keywords: sport pedagogy – sport initiation – game – reflexive teaching Este trabajo aparece de la necesidad de discusiones a respecto del papel educativo del profesional de educación física en la ense anza deportiva y Pedagogía del deporte. Relacionamos las corrientes teóricas de la pedagogía del deporte con la ense anza de los juegos colectivos. Para eso, utilizamos como instrumento el juego, la herramienta básica de la ense anza y la oportunidad social, por medio de sus características lúdicas. El juego puede contribuir en el desarrollo de valores éticos, sociales y morales; como también en la construcción de metáforas que establecen relaciones entre el deporte y la vida, haciendo uso de lo lúdico y la educación reflexiva. Ambos fundamentan nuestro basamiento teórico para el funcionamiento en Pedagogía del deporte, trayendo más oportunidades, opciones de elección y reflexiones en nuestra actuación profesional. PALABRAS-CLAVE: Pedagogía del deporte – iniciación deportiva – juego – educación reflexiva.
Distress influence in fibromyalgia
S. Stisi,C. Venditti,I. Saracco
Reumatismo , 2011, DOI: 10.4081/reumatismo.2008.274
Abstract: Objective: Fibromyalgia syndrome (FM) is a controversial chronic painful syndrome. Although the aetiology is unknown, FM is frequently correlated with stressors events. Recent studies highlighted the frequent comorbidity with anxiety and depression and a close relationship between stress and pain. Methods: We evaluated the relevance of stressors events in 23 patients with FM (mean age: 45.7±7.4 SD), compared with 18 healthy controls (mean age: 41.7±6.4 SD) and 17 patients with dysfunctional syndrome (mean age 40.8±6.1). We performed the italian validated rapid assessment of the stress test (VRS) for the assessment of stress. Furthermore, we evaluated the psychological history for a semi-quantitative assessment (IVAS) of the 49 stress-generating events listed in 1994’s DSM-IV. Results: The group of “healthy” subjects showed stress values at VRS test (mean: 7.00±4.65 SD) significantly lower (p=0.0001) than the patients with “dysfunctional syndrome“ (mean 14.82±7.69 SD) and those with FM (mean 20.04±9.90 SD). The IVAS test, showed higher values in FM subgroup than healthy (p=0.0001) and dysfunctional syndromes (p=0,007). Also, the patients with FM showed a greater gravity to attribute to single stressors events (p=0.02). Conclusions: Our results emphasize the importance of the perceived stress among the patients with FM, and support the hypothesis that FM could be due to a psycho-neuro-endocrinal response to several stressors events in patients with genetical hyperresponsiveness to stress.
Microphone Diversity Combining for In-Car Applications
Freudenberger Jürgen,Stenzel Sebastian,Venditti Benjamin
EURASIP Journal on Advances in Signal Processing , 2010,
Abstract: This paper proposes a frequency domain diversity approach for two or more microphone signals, for example, for in-car applications. The microphones should be positioned separately to insure diverse signal conditions and incoherent recording of noise. This enables a better compromise for the microphone position with respect to different speaker sizes and noise sources. This work proposes a two-stage approach. In the first stage, the microphone signals are weighted with respect to their signal-to-noise ratio and then summed similar to maximum ratio combining. The combined signal is then used as a reference for a frequency domain least-mean-squares (LMS) filter for each input signal. The output SNR is significantly improved compared to coherence-based noise reduction systems, even if one microphone is heavily corrupted by noise.
The Disclosure of University Research for Third Parties: A Non-Market Perspective on an Italian University
Michelina Venditti,Emanuela Reale,Loet Leydesdorff
Computer Science , 2011,
Abstract: Nations, universities, and regional governments commit resources to promote the dissemination of scientific and technical knowledge. One focuses on knowledge-based innovations and the economic function of the university in terms of technology transfer, intellectual property, university-industry-government relations, etc. Faculties other than engineering or applied sciences, however, may not be able to recognize opportunities in this "linear model" of technology transfer. We elaborate a non-market perspective on the third mission in terms of disclosure of the knowledge and areas of expertise available for disclosure to other audiences at a provincial university. The use of ICT can enhance communication between actors on the supply and demand sides. Using an idea originally developed in the context of the Dutch science shops, the university staff was questionnaired about keywords and areas of expertise with the specific purpose of disclosing this information to audiences other than academic colleagues. The results were brought online in a thesaurus-like structure that enables users to access the university at the level of individual email address. This model stimulates variation on both the supply and demand side of the innovation process, and strengthens the accessibility and embeddedness of the knowledge base in a regional economy.
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