Galaxy groups in the 2dF galaxy redshift survey: Large Scale Structure with Groups

We use the 2dF Galaxy Group Catalogue constructed by Merch\'an & Zandivarez to study the large scale structure of the Universe traced by galaxy groups. We concentrate on the computation of the power spectrum and the two point correlation function. The resulting group power spectrum shows a similar shape to the galaxy power spectrum obtained from the 2dF Galaxy Redshift Survey by Percival et al., but with a higher amplitude quantified by a relative bias in redshift space of $b_s(k) \sim 1.5$ . The group two point correlation function for the total sample is well described by a power law with correlation length s_0=8.9 \pm 0.3 \mpc and slope $\gamma=-1.6 \pm 0.1$ on scales s < 20 \mpc. In order to study the dependence of the clustering properties on group mass we split the catalogue in four subsamples defined by different ranges of group virial masses. These computations allow a fair estimate of the relation described by the correlation length $s_0$ and the mean intergroup separation $d_c$ for galaxy systems of low mass. We also extend our study to the redshift space distortions of galaxy groups, where we find that the anisotropies in the clustering pattern of the 2dF group catalogue are consistent with gravitational instability, with a flattening of the redshift-space correlation function contours in the direction of the line of sight.Comment: 11 pages, 9 figures, resubmitted to MNRAS after revisio

Computation of conical intersections by using perturbation techniques

Multiconfigurational second-order perturbation theory, both in its single-state multiconfigurational second-order perturbation theory (CASPT2) and multistate (MS-CASPT2) formulations, is used to search for minima on the crossing seams between different potential energy hypersurfaces of electronic states in several molecular systems. The performance of the procedures is tested and discussed, focusing on the problem of the nonorthogonality of the single-state perturbative solutions. In different cases the obtained structures and energy differences are compared with available complete active space self-consistent field and multireference configuration interaction solutions. Calculations on different state crossings in LiF, formaldehyde, the ethene dimer, and the penta-2,4-dieniminium cation illustrate the discussions. Practical procedures to validate the CASPT2 solutions in polyatomic systems are explored, while it is shown that the application of the MS-CASPT2 procedure is not straightforward and requires a careful analysis of the stability of the results with the quality of the reference wave functions, that is, the size of the active [email protected] [email protected] [email protected]

Dynamical segregation of galaxies in groups and clusters

We have performed a systematic analysis of the dynamics of different galaxy populations in galaxy groups from the 2dFGRS. For this purpose we have combined all the groups into a single system, where velocities v and radius r are expressed adimensionally. We have used several methods to compare the distributions of relative velocities of galaxies with respect to the group centre for samples selected according to their spectral type (as defined by Madgwick et al., 2002), bj band luminosity and B-R colour index. We have found strong segregation effects: spectral type I objects show a statistically narrower velocity distribution than that of galaxies with a substantial star formation activity (type II-IV). Similarly, the same behavior is observed for galaxies with colour index B-R>1 compared to galaxies with B-R<1. Bright (Mb-19) galaxies show the same segregation. It is not important once the sample is restricted to a given spectral type. These effects are particularly important in the central region (Rp<Rvirial/2) and do not have a strong dependence on the mass of the parent group. These trends show a strong correlation between the dynamics of galaxies in groups and star formation rate reflected both by spectral type and by colour index.Comment: 7 pages, 8 figures. Accepted for publication in MNRA

Theoretical characterization of the lowest-energy absorption band of pyrrole

The lowest-energy band of the electronic spectrum of pyrrole has been studied with vibrational resolution by using multiconfigurational second-order perturbation theory (CASPT2) and its multistate extension (MS–CASPT2) in conjunction with large atomic natural orbital-type basis sets including Rydberg functions. The obtained results provide a consistent picture of the recorded spectrum in the energy region 5.5–6.5 eV and confirm that the bulk of the intensity of the band arises from a ππ∗ intravalence transition, in contradiction to recent theoretical claims. Computed band origins for the 3s,3p Rydberg electronic transitions are in agreement with the available experimental data, although new assignments are suggested. As illustrated in the paper, the proper treatment of the valence–Rydberg mixing is particularly challenging for ab initio methodologies and can be seen as the main source of deviation among the recent theoretical results as regards the position of the low-lying valence excited states of [email protected] ; [email protected]

Ab initio study on the low-lying excited states of retinal

Ab initio results for the electronic spectrum of all-trans-retinal and its truncated model 3-methyl-all-trans (10-s-cis)-2,4,6,8,10-undecapentaen-1-al are presented. The study includes geometry determination of the ground state. Vertical excitation energies have been computed using multiconfigurational second-order perturbation theory through the CASPT2 formalism. The lowest singlet excited state in gas phase is predicted to be of nπ∗ character. The lowest triplet state corresponds, however, to a ππ∗ state. The most intense feature of the spectrum is due to the strongly dipole-allowed ππ∗ transition, in accordance with the observed maximum in the one-photon spectra. The vertical excitation energies of the Bu- and Ag-like states are found close, the latter ≈ 1 eV higher than the maximum in the two-photon spectra. Solvent effects and nonvertical nature of the observed maximum in the two-photon spectra are invoked in rationalizing the deviation with respect to the best present estimate for the Ag-like state. In addition, qualitative aspects of the one-bond photoisomerization about the C11 = C12 double bond of retinal are considered. The overall isomerization picture from 11-cis into all-trans-retinal, as taking place mainly along the triplet manifold, agrees with experimental [email protected] ; [email protected]

Galaxy interactions II: High density environments

With the aim to assess the role of dense environments in galaxy interactions, properties we present an analysis of close galaxy pairs in groups and clusters, obtained from the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7). We identified pairs that reside in groups by cross-correlating the total galaxy pair catalogue with the SDSS-DR7 group catalogue from Zapata et al. (2009). We classify pair galaxies according to the intensity of interaction. We analysed the effect of high density environments on different classes of galaxy-galaxy interactions and we have also studied the impact of the group global environment on pair galaxies. We find that galaxy pairs are more concentrated towards the group centres with respect to the other group galaxy members, and disturbed pairs show a preference to contain the brightest galaxy in the groups. The color-magnitude relation exhibits significant differences between pair galaxies and the control sample, consisting in color tails with a clear excess of extremely blue and red galaxies for merging systems. In addition, pair galaxies show a significant excess of young stellar populations with respect to galaxies in the control sample; this finding suggests that, in dense environments, strong interactions produce an important effect in modifying galaxy properties. We find that the fraction of star forming galaxies decreases toward the group centre; however, galaxy pairs show a more efficient star formation activity than galaxies without a close companion. We have also found that pair galaxies prefer groups with low density global environments with respect to galaxies of the corresponding control sample. Blue, young stellar population galaxies prefer groups within low density global environments.Comment: 10 pages, 11 figures, accepted for publication in A&

Importancia del conocimiento empírico en obras civiles

This article is presented on the importance of empirical knowledge in order to make known the need, incidence and application of such knowledge in civil works. In addition, it is made with the purpose of documenting the subject that involves masters of work, engineers, workers and other participants of work, but that does not count with diffusion. The article was mostly written at the Universidad Distrital Francisco José de Caldas, Facultad Tecnológica, with the support of workers from the area, master builders, civil engineers and other participants in the work at the university and in the surrounding areas. It established the need for empirical thinking and made it clear that it is not the only thing necessary for good performance in civil works, reaching the conclusion that empirical knowledge and academic knowledge are necessary to perform in the best way in civil works because both knowledge are important for certain moments of working life.Se presenta este artículo sobre la importancia del conocimiento empírico con el fin de dar a conocer la necesidad, incidencia y aplicación de dicho conocimiento en obras civiles. Además, se realiza con el fin de documentar sobre el tema que involucra a maestros de obra, ingenieros, obreros y demás participantes de obra, pero que no cuanta con difusión. El artículo se realizó mayormente en la Universidad Distrital Francisco José de Caldas, Facultad Tecnológica con el apoyo de obreros de la zona, maestros de obra, ingenieros civiles y demás participantes de obras en la universidad y en zonas aledañas. Se establecieron necesidades del pensamiento empírico y se dejó claro que no es lo único necesario para un buen desempeño en obra civiles, llegando a la conclusión de que el conocimiento empírico y el conocimiento académico son necesarios para desempeñarse de la mejor manera en obras civiles pues ambos conocimientos son importantes para ciertos momentos de la vida laboral