1,721,006 research outputs found
Molecules in the postrecombination universe and microwave background anisotropies
No full textWe consider the effects of the elastic Thomson scattering between cosmic background radiation (CBR) and primordial molecules, like H2, H2(+), HeH(+), HD, HD(+), LiH, LiH(+): primary CBR anisotropies may be erased or attenuated for angular scales is less than or equal to 10 deg up to 50 deg and frequencies nu is less than or equal to 50 GHz, if LiH primordial abundance exceed 10-10(H). Conversely, CBR anisotropy data may be used to put stringent upper limits on the abundance of primordial elements. Already available data on CBR anisotropies at various frequencies impose primordial LiH abundance to be not larger than 2 x 10-9(H). Secondary anisotropies are expected at arcsecond-arcminute angular scales, due to the anisotropic scattering by moving molecular clouds: they are stronger in the millimetric region and close to be detected in IRAM 200 GHz observations
Molecular signals from primordial clouds at high redshift
No full textThe possibility of detecting cosmological signals from the postrecombination universe is one of the main aims of modern cosmology. In a previous paper we emphasized the role that elastic resonant scattering through WH molecules can have in dumping primary cosmic background radiation (CBR) anisotropies and raising secondary signals. Here we extend our analysis to all the evolutionary stages of a primordial cloud, starting with the linear phase, through the turnaround, and to the nonlinear collapse. We have done calculations for protoclouds in a cold dark matter (CDM) scenario and, more generally, for a set of clouds with various masses and various turnaround redshifts, in this case without referring to any particular structure formation scenario. We found that the first phase of collapse, for t/t(free-fall) = 0.05-0.2 is the best one for simultaneous detection of the first two LiH rotational lines. The observational frequency falls between 30 and 250 GHz, and the line width Delta nu/nu is between 10(-5) and 10(-4). As far as we know, this is the most favorable process to detect primordial clouds before they begin star formation processes
Weak lensing halo detection by Euclid
No full textIt has been widely shown that weak lensing surveys can be used for detecting dark matter concentrations. Here we use the aperture mass method to predict the detectability and number density of cluster-sized halos from a weak lensing survey as expected from the future space-based Euclid mission. The method bases on the image distortion of background galaxies caused by the gravitational potential of intervening dark matter distribution. Preliminary results on the expected number density of halos with a given signal-to-noise ratio are presented for different cosmologies, showing how halo number counts can be a useful probe to discriminate among different cosmological models
2K1BC Workshop "Experimental Cosmology at millimetre wavelengths"
No full textThe 2K1BC Workshop was a meeting of scientists from all over the world involved in cosmological observations in the millimetre wavelength range. Current and upcoming experiments were reported with present results and future forecasts: balloon borne projects which have detected the tiny temperature fluctuations in cosmic microwave background radiation (CMBR); satellite programs that promise to give a clearer picture of observational cosmology; as well as ground-based observations which are the necessary complement to these projects. A separate section is devoted to the CMBR polarization that seems to be the main challenge in the near future. Particular attention was devoted to specific instrumental topics (optics, cryogenics, and detectors) and observational techniques
Franceso Melchiorri: Scientist, Pioneer, Mentor - Proceedings of the Francesco Melchiorri Memorial Conference, Department of Physics, University of Rome "La Sapienza", Rome, Italy, 12-14 April 2006 - Foreword
No full textImproving lensing cluster mass estimate with flexion
No full textGravitational lensing has long been considered as a valuable tool to determine the total mass of galaxy clusters. The shear profile, as inferred from the statistics of ellipticity of background galaxies, allows us to probe the cluster intermediate and outer regions, thus determining the virial mass estimate. However, the mass sheet degeneracy and the need for a large number of background galaxies motivate the search for alternative tracers which can break the degeneracy among model parameters and hence improve the accuracy of the mass estimate. Lensing flexion, i.e. the third derivative of the lensing potential, has been suggested as a good answer to the above quest since it probes the details of the mass profile. We investigate here whether this is indeed the case considering jointly using weak lensing, magnification and flexion. We use a Fisher matrix analysis to forecast the relative improvement in the mass accuracy for different assumptions on the shear and flexion signal-to- noise (S/N) ratio also varying the cluster mass, redshift, and ellipticity. It turns out that the error on the cluster mass may be reduced up to a factor of ̃2 for reasonable values of the flexion S/N ratio. As a general result, we get that the improvement in mass accuracy is larger for more flattened haloes, but it extracting general trends is difficult because of the many parameters at play. We nevertheless find that flexion is as efficient as magnification to increase the accuracy in both mass and concentration determination
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
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