Non-linear Matter Spectra in Coupled Quintessence

We consider cosmologies in which a dark-energy scalar field interacts with cold dark matter. The growth of perturbations is followed beyond the linear level by means of the time-renormalization-group method, which is extended to describe a multi-component matter sector. Even in the absence of the extra interaction, a scale-dependent bias is generated as a consequence of the different initial conditions for baryons and dark matter after decoupling. The effect is enhanced significantly by the extra coupling and can be at the 2-3 percent level in the range of scales of baryonic acoustic oscillations. We compare our results with N-body simulations, finding very good agreement.Comment: 20 pages, 6 figures, typo correcte

Hadron and Quark Form Factors in the Relativistic Harmonic Oscillator Model

Nucleon, pion and quark form factors are studied within the relativistic harmonic oscillator model including the quark spin. It is shown that the nucleon charge, magnetic and axial form factors and the pion charge form factor can be explained with one oscillator parameter if one accounts for the scaling rule and the size of the constituent quarks.Comment: 9 pages, Latex, 3 postscript figures, DFTT 8/9

Irreversible phase transitions induced by an oscillatory input

A novel kind of irreversible phase transitions (IPT's) driven by an oscillatory input parameter is studied by means of computer simulations. Second order IPT's showing scale invariance in relevant dynamic critical properties are found to belong to the universality class of directed percolation. In contrast, the absence of universality is observed for first order IPT's.Comment: 18 pages (Revtex); 8 figures (.ps); submitted to Europhysics Letters, December 9th, 199

The Cheeger problem in abstract measure spaces

We consider nonnegative (Formula presented.) -finite measure spaces coupled with a proper functional (Formula presented.) that plays the role of a perimeter. We introduce the Cheeger problem in this framework and extend many classical results on the Cheeger constant and on Cheeger sets to this setting, requiring minimal assumptions on the pair measure space perimeter. Throughout the paper, the measure space will never be asked to be metric, at most topological, and this requires the introduction of a suitable notion of Sobolev spaces, induced by the coarea formula with the given perimeter

ClustOfVar: An R Package for the Clustering of Variables

Clustering of variables is as a way to arrange variables into homogeneous clusters, i.e., groups of variables which are strongly related to each other and thus bring the same information. These approaches can then be useful for dimension reduction and variable selection. Several specific methods have been developed for the clustering of numerical variables. However concerning qualitative variables or mixtures of quantitative and qualitative variables, far fewer methods have been proposed. The R package ClustOfVar was specifically developed for this purpose. The homogeneity criterion of a cluster is defined as the sum of correlation ratios (for qualitative variables) and squared correlations (for quantitative variables) to a synthetic quantitative variable, summarizing "as good as possible" the variables in the cluster. This synthetic variable is the first principal component obtained with the PCAMIX method. Two algorithms for the clustering of variables are proposed: iterative relocation algorithm and ascendant hierarchical clustering. We also propose a bootstrap approach in order to determine suitable numbers of clusters. We illustrate the methodologies and the associated package on small datasets

Lutheran Social Services service learning project

Background: Lutheran Social Services (LSS) is an organization whose mission is to “express the love of Christ for all people through service that inspires hope, changes lives, and builds community.” A significant part of what they do involves leading afterschool activities that promote the learning of specific academic and life skills. Those learning objectives are as stated as follows: (1) working together, (2) communication, (3) following instructions, and (4) personal boundaries. As liberal arts students, we provide external perspectives regarding ways to enhance their four learning objectives. Because they have our help in developing new leisure activities for their students, the LSS staff has more time at their disposal to focus on improving other aspects of the program. Our help in creating exciting new games was also useful simply because they were novel experiences for the children, coming from different sources than what they were used to; that is, the kids had the opportunity to experience various games they may not have played before. Additionally, the staff gained a new perspective on different follow-up discussion questions for the children after every game. Overall, our goal was to help make LSS a more fun and productive site in any way we were able to achieve. Those games help make the site an empowering setting by allowing the kids to participate in activities and share power in group activities. They also get to have fun doing it. The facility is a converted house. The project came about because the LSS staff needed different viewpoints on how to accomplish their learning objectives for their kids. They reported that it was great for the kids to experience new games from different standpoints. Though our intervention was implemented at the Sauk Rapids LSS site, almost all of our work came from home. The project was designed for about 15 children aged 9 to 13 who were enrolled in Lutheran Social Services’ afterschool Kid’s Resiliency Program (KRP). The children had either mental disabilities or learning disorders. They all have different interests and abilities; therefore, we created a host of different games in an attempt to satisfy all their needs. We visited the site to meet the staff and visually assess our population’s needs

Damage Spreading in a Driven Lattice Gas Model

We studied damage spreading in a Driven Lattice Gas (DLG) model as a function of the temperature $T$, the magnitude of the external driving field $E$, and the lattice size. The DLG model undergoes an order-disorder second-order phase transition at the critical temperature $T_c(E)$, such that the ordered phase is characterized by high-density strips running along the direction of the applied field; while in the disordered phase one has a lattice-gas-like behaviour. It is found that the damage always spreads for all the investigated temperatures and reaches a saturation value $D_{sat}$ that depends only on $T$. $D_{sat}$ increases for $TT_c(E=\infty)$ and is free of finite-size effects. This behaviour can be explained as due to the existence of interfaces between the high-density strips and the lattice-gas-like phase whose roughness depends on $T$. Also, we investigated damage spreading for a range of finite fields as a function of $T$, finding a behaviour similar to that of the case with $E=\infty$.Comment: 13 pages, 7 figures. Submitted to "Journal of Statistical Mechanics: Theory and Experiment

Extremely compact massive galaxies at z~1.4

The optical rest-frame sizes of 10 of the most massive (~5x10^{11}h_{70}^{-2}M_sun) galaxies found in the near-infrared MUNICS survey at 1.2<z<1.7 are analysed. Sizes were estimated both in the J and K' filters. These massive galaxies are at least a factor of 4_{-1.0}^{+1.9} (+-1 sigma) smaller in the rest-frame V-band than local counterparts of the same stellar mass. Consequently, the stellar mass density of these objects is (at least) 60 times larger than massive ellipticals today. Although the stellar populations of these objects are passively fading, their structural properties are rapidly changing since that redshift. This observational fact disagrees with a scenario where the more massive and passive galaxies are fully assembled at z~1.4 (i.e. a monolithic scenario) and points towards a dry merger scenario as the responsible mechanism for the subsequent evolution of these galaxies.Comment: 5 pages, 2 figures, 1 table, accepted for publication in MNRAS letter

Triplets of Quasars at high redshift I: Photometric data

We have conducted an optical and infrared imaging in the neighbourhoods of 4 triplets of quasars. R, z', J and Ks images were obtained with MOSAIC II and ISPI at Cerro Tololo Interamerican Observatory. Accurate relative photometry and astrometry were obtained from these images for subsequent use in deriving photometric redshifts. We analyzed the homogeneity and depth of the photometric catalog by comparing with results coming from the literature. The good agreement shows that our magnitudes are reliable to study large scale structure reaching limiting magnitudes of R = 24.5, z' = 22.5, J = 20.5 and Ks = 19.0. With this catalog we can study the neighbourhoods of the triplets of quasars searching for galaxy overdensities such as groups and galaxy clusters.Comment: The paper contains 12 figures and 3 table