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Search Results: 1 - 10 of 663771 matches for " A. J; Martins "
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On a connection between gravitation and quantum chromodynamics
J. A. Martins Simoes
Physics , 2004,
Abstract: In this paper we point out a remarkable numerical relation between the large scale parameters of gravitation G_N and H_0 and the two fundamental parameters of quantum cromodynamics alpha_{QCD} and Lambda_{QCD}. With this remark we make the conjecture that Newton's gravitational constant could show an energy dependence analogous to alpha_{QCD}.
Bioacoustic analysis of advertisement call in Hyla nana and Hyla sanborni (Anura, Hylidae) in Botucatu, S?o Paulo, Brazil
Martins, I. A.;Jim, J.;
Brazilian Journal of Biology , 2003, DOI: 10.1590/S1519-69842003000300017
Abstract: vocal communication traits of hyla nana and hyla sanborni, of the nana species group, were studied from august 1997 until june 1999 in two large permanent ponds located in an open field in botucatu, s?o paulo state. one hundred thirty-one individuals, 71 of h. nana and 58 of h. sanborni, were recorded in the beginning of their vocalization activity and during chorus vocalization. the rhythms of sound emission on the two occasions were different. an advertisement call consists in a consecutive series of simple notes in rapid succession. both species have two types of notes in their advertisement calls, here named types a and b. type a notes are introductory and have a longer and higher pulse number and are emitted more frequently in the beginning of vocalization activity. introductory notes are the first to be emitted in chorus activity. type b notes are secondary, of shorter duration and lower pulse number, and are emitted during chorus vocalization. the notes of both types differ significantly in their temporal structure. both species present acoustic segregation in both spectral and temporal structure.
Advertisement call of Hyla jimi and Hyla elianeae (Anura, Hylidae) in the Botucatu Region, S?o Paulo, Brazil
Martins, I. A.;Jim, J.;
Brazilian Journal of Biology , 2004, DOI: 10.1590/S1519-69842004000400012
Abstract: in this work we present a description of the advertisement call of h. jimi, the locality type, and of h. elianeae, until now unknown in the literature. field activities were carried out from august 1997 through june 1999; recordings were made in two open-area environments in the botucatu region, s?o paulo state. vocalizations of 100 individuals (49 h. jimi and 51 h. elianeae) were recorded; nine characteristics of the advertisement call were examined. the advertisement calls of both species consist of consecutive series of simple notes with relatively fast repetition rates. males of h. jimi and h. elianeae presented two patterns of note emission: one emitted by individuals beginning vocalization activity or isolated from the aggregate, and another emitted by males in chorus activity interacting with closely neighboring males. a significant difference was verified in the temporal structure of the two vocalization patterns.
Bioacoustic analysis of advertisement call in Hyla nana and Hyla sanborni (Anura, Hylidae) in Botucatu, S o Paulo, Brazil
Martins I. A.,Jim J.
Brazilian Journal of Biology , 2003,
Abstract: Vocal communication traits of Hyla nana and Hyla sanborni, of the nana species group, were studied from August 1997 until June 1999 in two large permanent ponds located in an open field in Botucatu, S o Paulo State. One hundred thirty-one individuals, 71 of H. nana and 58 of H. sanborni, were recorded in the beginning of their vocalization activity and during chorus vocalization. The rhythms of sound emission on the two occasions were different. An advertisement call consists in a consecutive series of simple notes in rapid succession. Both species have two types of notes in their advertisement calls, here named types A and B. Type A notes are introductory and have a longer and higher pulse number and are emitted more frequently in the beginning of vocalization activity. Introductory notes are the first to be emitted in chorus activity. Type B notes are secondary, of shorter duration and lower pulse number, and are emitted during chorus vocalization. The notes of both types differ significantly in their temporal structure. Both species present acoustic segregation in both spectral and temporal structure.
String Evolution in Open Universes
C. J. A. P. Martins
Physics , 1997, DOI: 10.1103/PhysRevD.55.5208
Abstract: The velocity-dependent `one-scale' model of Martins and Shellard is used to study the evolution of a cosmic string network (and the corresponding loop population) in open universes. It is shown that in this case there is no linear scaling regime and that even though curvature still dominates the dynamics, at late times strings become the main component of the universe. We also comment on the possible consequences of these results.
New Constraints on Varying Alpha
C. J. A. P. Martins
Physics , 2004,
Abstract: I briefly present some current theoretical motivations for time or space variations of the fundamental constants of nature and review current key observational results. I focus on the fine-structure constant, and particularly on measurements using quasars and the cosmic microwave background. I also compare various observational results to the simplest model-building expectations.
Three tests of LambdaCDM
C. J. A. P. Martins
Physics , 2012,
Abstract: The observational evidence for the acceleration of the universe demonstrates that canonical theories of gravitation and particle physics are incomplete, if not incorrect. The next generation of astronomical facilities must both be able to carry out precision consistency tests of the standard cosmological model and search for evidence of new physics beyond it. I describe some of these tests, and discuss prospects for facilities in which the CAUP Dark Side team is involved, specifically ESPRESSO, Euclid and CODEX.
Scaling properties of cosmic (super)string networks
C. J. A. P. Martins
Physics , 2013, DOI: 10.1088/1742-6596/544/1/012026
Abstract: I use a combination of state-of-the-art numerical simulations and analytic modelling to discuss the scaling properties of cosmic defect networks, including superstrings. Particular attention is given to the role of extra degrees of freedom in the evolution of these networks. Compared to the 'plain vanilla' case of Goto-Nambu strings, three such extensions play important but distinct roles in the network dynamics: the presence of charges/currents on the string worldsheet, the existence of junctions, and the possibility of a hierarchy of string tensions. I also comment on insights gained from studying simpler defect networks, including Goto-Nambu strings themselves, domain walls and semilocal strings.
Scaling Laws for Non-Intercommuting Cosmic String Networks
C. J. A. P. Martins
Physics , 2004, DOI: 10.1103/PhysRevD.70.107302
Abstract: We study the evolution of non-interacting and entangled cosmic string networks in the context of the velocity-dependent one-scale model. Such networks may be formed in several contexts, including brane inflation. We show that the frozen network solution $L\propto a$, although generic, is only a transient one, and that the asymptotic solution is still $L\propto t$ as in the case of ordinary (intercommuting) strings, although in the present context the universe will usually be string-dominated. Thus the behaviour of two strings when they cross does not seem to affect their scaling laws, but only their densities relative to the background.
Extra Dimensions and Varying Alpha
C. J. A. P. Martins
Physics , 2002,
Abstract: I review recent constraints on and claimed detections of a time-varying fine-structure constant $\alpha$. Our results are consistent with no variation in $\alpha$ from the epoch of recombination to the present day, and restrict any such variation to be less than about 4%. The forthcoming MAP and Planck experiments will be able to break most of the currently existing degeneracies between $\alpha$ and other cosmological parameters, and measure $\alpha$ in the early universe with an accuracy comparable to current claimed recent-universe detections.
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