56302496
Design, analysis, and fabrication of the APT cavities
The design for the superconducting cavities of the high-energy accelerator for the Accelerator Production of Tritium (APT) project has been extensively changed in the last two years. The original accelerator design incorporated 0.48 and 0.71 beta cavities with stiffeners, and a stainless-steel helium vessel. Today, the accelerator uses unstiffened 0.64 and 0.82 beta cavities, and a titanium helium vessel. This paper discusses the design process, including the supporting analyses, prototype cavities built, and the decisions made to support the current design. The design of the integrated cavity-helium vessel is presented. Future plans and testing for design validation are also discussed.
117082338
Review of the Second School on Cosmic Rays and Astrophysics
54807942
Self-similarity in a Kantowski-Sachs universe with a string cloud
We study a cosmological model with very simple solutions characterized by string clouds. Assuming self-similar symmetry for a Kantowski- Sachs spacetime we study the gravitational effects of the cosmic strings. It is also assumed that the primitive universe enters in a false vacuum-dominated era, accelerating the expansion in a time period of the order of 10 -35 sec (a phase transition), satisfying all the energy conditions. Finally, we examine the possibility that in the last stages of this evolution, the geometry of the universe could be flat.
118112489
Air Shower Simulations
Air shower simulations are a vital part of the design of air shower experiments and the analysis of their data. We describe the basic features of air showers and explain why numerical simulations are the appropriate approach to model the shower simulation. The CORSIKA program, the standard simulation program in this field, is introduced and its features, performance and limitations are discussed. The basic principles of hadronic interaction models and some gerneral simulation techniques are explained. Also a brief introduction to the installation and use of CORSIKA is given.
17504603
Using the large scale quasar clustering to constrain flat quintessential universes
Aims. We search for the most suitable set of cosmological parameters that describes the observable universe. The search includes the possibility of quintessential flat universes, i.e., the analysis is restricted to the determination of the dimensionless matter density and the quintessential parameters, $\Omega_{\rm M}$ and w Q , respectively. Methods. Our study is focused on comparing the position of features at large scales in the density fluctuation field at different redshifts by analysing the evolution of the quasar two-point correlation function. We trace the density field fluctuations at large scales using a large and homogeneous sample of quasars (~38 000 objects with 0.3  ≲ z ≤  2.4 and a median z = 1.45) drawn from the Sloan Digital Sky Survey Data Release Six. The analysis relies on the assumption that, in the linear regime, the length scale of a particular feature should remain fixed at different times of the universe for the proper cosmological model. Our study does not assume any particular comoving length scale at which a feature should be found, but intends to perform a comparison for a wide range of scales instead. This is done by quantifying the amount of overlap among the quasar correlation functions at different times using a cross-correlation technique. Results. The most likely cosmological model is $\Omega_{\rm M}$ = 0.21 ± 0.02 and w Q = -0.93 ± 0.04, in agreement with previous studies. These constraints are the result of a good overall agreement of the correlation function at different redshifts over scales ~100–300 h -1 Mpc. Conclusions. Under the assumption of a flat cosmological model, our results indicate that we are living in a low density universe with a quintessential parameter greater than the one corresponding to a cosmological constant. This work also demonstrates that a large homogeneous quasar sample can be used to tighten the constraints upon cosmological parameters.
14358536
Groups of galaxies: relationship between environment and galaxy properties
We analyse how the properties of galaxies in groups identified in the Sloan Digital Sky Survey depend on the environment. In particular, we study the relationship between galaxy properties and group mass and group-centric distance. Among the galaxy properties we have considered here, we find that the g - r colour is the most predictive parameter for group mass, while the most predictive pair of properties are g - r colour and r-band absolute magnitude. Regarding the position inside the systems, the g - r colour is the best tracer of group-centric distance and the most predictive pair of properties are g - r colour and spectral type taken together. These results remain unchanged when a subsample of high-mass groups is analysed. The same happens if the brightest group galaxies are excluded.
117908138
COMPARING GALAXY POPULATIONS IN COMPACT AND LOOSEGROUPS OF GALAXIES
Aims. We compare the properties of galaxies in compact groups, loose groups, and the field to deepen our understanding of the physical mechanisms acting upon galaxy evolution in different environments. Methods. We select samples of galaxies in compact groups, loose groups, and field galaxies from the Sloan Digital Sky Survey. We compare the properties of the galaxy populations in these different environments: absolute magnitude, colour, size, surface brightness, stellar mass, and concentration. We also study the fraction of red and early-type galaxies, the luminosity function, the colourluminosity, and luminosity-size relations. Results. The population of galaxies in compact groups differ from that of loose groups and the field. The fraction of red and early-type galaxies is larger in compact groups. Galaxies in compact groups are, on average, systematically smaller in size, more concentrated, and have higher surface brightnesses than galaxies in the field and in loose groups. At a fixed absolute magnitude, or fixed surface brightness, galaxies in compact groups are smaller in size. Conclusions. The physical mechanisms that transform galaxies into earlier types could be more effective within compact groups, owing to the typically high densities and small velocity dispersions of these environments, which could explain the large fraction of red and early-type galaxies we found in compact groups. Galaxies inhabiting compact groups have undergone a major transformation compared to galaxies that inhabit loose groups.