The Association of Compact Groups of Galaxies with Large-scale Structures

We use various samples of compact groups (CGs) to examine the types of association CGs have with rich and poor clusters of galaxies at low (z~0.04) and intermediate (z~0.1) redshifts. We find that ~10-20 % of CGs are associated with rich clusters and a much larger fraction with poorer clusters or loose groups. Considering the incompleteness of catalogs of poorer systems at intermediate redshift, our result is consistent with all CGs at intermediate redshift being associated with larger-scale systems. The richness of the clusters associated with CGs significantly increases from z~0.04 to z~0.1, while their Bautz-Morgan type changes from early to late type for the same range in z. Neither trend is compatible with a selection effect in the cluster catalogs used. We find earlier morphological types of galaxies to be more frequent in CGs associated with larger-scale structures, compared to those in CGs not associated to such structures. We consider this as new evidence that CGs are part of the large-scale structure formation process and that they may play an important role in the evolution of galaxies in these structures.Comment: 5 pages, no figures, Proc. ESO Workshop "Groups of galaxies in the nearby Universe", Santiago, Chile, 5-9 Dec. 2005, ESO Astrophysics Symposia, eds. I. Saviane, V. Ivanov & J. Borissova, Springer-Verlag; very minor revision of text on 15 Mar 2006, added one referenc

Evaluation of soil physical quality under different soil land uses in a small Sicilian watershed

Sustainability of extensive rain fed agriculture needs assessment of land use effects on soil physical and hydraulic properties. Several soil physical quality indices were determined for four adjacent areas in a small Sicilian watershed, that were characterized by a different land use, namely cropland (C), olive grove (O), grassland (G) and eucalyptus plantation (E). Soil texture was similar for the considered areas, even if the no-tilled soils (G and E) showed a higher clay content in the top layer (0-20 cm) than in the lower layer (20-40 cm). The bulk density of the top layer ranged between 1.20-1.43 g cm-3 (C < G < O < E), with significant differences between C and E. In the lower layer, it ranged between 1.16-1.43 g cm-3 (C < O < E < G), with bulk density of C that was significantly smaller than that of the other land uses. The organic matter content was generally low and comparable for the different areas (in average 1.6%). The near-saturated soil hydraulic conductivity values were significantly higher for no-tilled (G, E) than tilled soils (C, O), whereas the opposite result was found for smaller degrees of saturation. The Dexter’s soil quality index assumed similar values in both the top (0.024-0.047) and the lower layer (0.024-0.040), with the higher values associated to tilled soils. According to existing guidelines, the soil physical quality of the selected areas was generally poor independently of the land use. However, the cropland showed a better quality than the other land uses

Dust Absorption and the Cosmic UV Flux Density

We study the evolution of the galaxy UV luminosity density as a function of redshift in the Hubble Deep Field North (HDF-N). We estimate the amount of energy absorbed by dust and hidden from optical observations by analyzing the HDF-N photometric data with the spectral energy distribution fitting method. According to our results, at redshifts 1 < z < 4.5, the global energy observed in the UV rest-frame at lambda=1500 A corresponds to only 7-11% of the stellar energy output, the rest of it being absorbed by dust and re-emitted in the far-IR. Our estimates of the comoving star formation rate density in the universe from the extinction-corrected UV emission are consistent with the recent results obtained with Submillimeter Common-User Bolometer Array (SCUBA) at faint sub-millimeter flux levels.Comment: 14 pages, 3 encapsulated postscript figures, LateX, accepted for publication in ApJ

A numerical test of soil layering effects on theoretical and practical Beerkan infiltration runs

With reference to a more compacted and less conductive upper soil layer overlying a less compacted and more conductive subsoil, a simple three-dimensional (3D) infiltration run is expected to yield more representative results of the upper layer than the subsoil. However, there is the need to quantitatively establish what is meant by more representativeness. At this aim, numerically simulated infiltration was investigated for a theoretically unconfined process under a null ponded head of water (d0H0 setup, with d = depth of ring insertion and H = ponded depth of water) and a practical Beerkan run (d1H1 setup, d = H = 1&nbsp;cm). The considered layered soils differed by both the layering degree (from weak to strong; subsoil more conductive than the upper soil layer by 2.3–32.4 times, depending on the layering degree) and the thickness of the upper soil layer (0.5–3&nbsp;cm). It was confirmed that water infiltration should be expected to be more representative of the upper soil layer when this layer is the less permeable since, for a 2-h experiment, the instantaneous infiltration rates for the layered soil were 1.0–2.1 times greater than those of the homogeneous low-permeable soil and 1.3–20.7 smaller than those of the homogeneous coarser soil that constituted the subsoil. Similarity with the homogeneous fine soil increased as expected as the upper layer became thicker. For a weak layering condition, the layered soil yielded an intermediate infiltration as compared with that of the two homogeneous soils forming the layered system. For a strong layering degree, the layered soil was more similar to the homogeneous fine soil than to the homogeneous coarse soil. Using the practical setup instead of the theoretical one should have a small to moderate effect on the instantaneous infiltration rates since all the calculated percentage differences between the d1H1 and d0H0 setups fell into the relatively narrow range of −18.8% to +17.4%. A sequential analysis procedure appeared usable to detect layering conditions but with some modifications as compared with the originally proposed procedure. The practical setup enhanced the possibility to recognize the time at which the characteristics of the subsoil start to influence the infiltration process. In conclusion, this investigation contributed to better interpret both the theoretical and the practically established 3D infiltration process in a soil composed of a less conductive upper soil layer overlying a more conductive subsoil and it also demonstrated that modifying the recently proposed sequential analysis procedure only using infiltration data could be advisable to determine the time when layering starts to influence the process

Correspondence between theory and practice of a Beerkan infiltration experiment

The Beerkan infiltration experiment is carried out by inserting the ring a short depth into the soil and establishing a positive head of water on the infiltration surface for at least a part of the run. Nevertheless, the data are analyzed by assuming a fully unconfined infiltration process (ring insertion depth, d&nbsp;=&nbsp;0 cm) and a null ponded depth of water (H&nbsp;=&nbsp;0 cm). The influence of ring insertion and ponded water on an infiltration process of 2&nbsp;h sampled every minute was tested in this numerical investigation. Five soils varying from sand to silt loam, three ring radii (5–15&nbsp;cm), and the Beerkan-specific range of values for both d and H (between 0 and 1&nbsp;cm) were considered. The differences between the theoretical (d&nbsp;=&nbsp;H&nbsp;=&nbsp;0 cm) and the practical (d&nbsp;=&nbsp;H&nbsp;=&nbsp;1&nbsp;cm) setups varied from −10.4 to +8.6% for the mean infiltration rate and from −10.2 to +8.3% for the final cumulative infiltration. These differences were small, and they decreased in absolute value by considering a soil-dependent ring radius. In particular, nearly negligible differences were detected using a small ring in coarse-textured soils and a large ring in fine-textured soils. In the coarser soils, inserting the ring and establishing a ponded depth of water did not alter the estimated coefficients of the two-parameter infiltration model appreciably with the cumulative linearization method, because these coefficients differed between the theoretical and practical setups by no more than 9.2%. In fine soils, linearization could not be possible regardless of the considered setup, or it was the use of d&nbsp;=&nbsp;H&nbsp;=&nbsp;1&nbsp;cm instead of d&nbsp;=&nbsp;H&nbsp;=&nbsp;0 cm that impeded a convincing linearization of the data. In conclusion, the good correspondence, in many circumstances, between the theoretical and the practical Beerkan infiltration experiment reinforced the interest in this simple experiment as a practical means to collect infiltration data in the field

Real Rigidity, Nominal Rigidity, and the Social Value of Information

Does welfare improve when firms are better informed about the state of the economy and can thus better coordinate their production and pricing decisions? We address this question in an elementary business-cycle model that highlights how the dispersion of information can impede both kinds of decisions and, in this sense, be the source of both real and nominal rigidity. Within this context we develop a taxonomy for how the social value of information depends on the two rigidities, on the sources of the business cycle, and on the conduct of monetary policy. (JEL D21, D82, D83, E32, E52

Do Quasars Lens Quasars?

If the unexpectedly high frequency of quasar pairs with very different component redshifts is due to the lensing of a population of background quasars by the foreground quasar, typical lens masses must be \sim10^{12}M_{\sun} and the sum of all such quasar lenses would have to contain $\sim0.005$ times the closure density of the Universe. It then seems plausible that a very high fraction of all \sim10^{12} M_{\sun} gravitational lenses with redshifts $z\sim1$ contain quasars. Here I propose that these systems have evolved to form the present population of massive galaxies with M$_{\rm B}\leq-22$ and M >5\times10^{11} M_{\sun}.Comment: 6 pages, aas style, ams symbols, ApJL (accepted

Impact of reforestations with exotic and native species on water repellency of forest soils

Forest duff layer is usually water repellent due to the hydrophobic organic compounds resulting from degradation of tree tissues. Transition from hydrophobic to wettable conditions, or vice versa, is largely controlled by water content. The objective of this investigation was to assess the influence of soil moisture on the degree of soil water repellency (WR) in exotic and native tree forests. Occurrence of WR was investigated by the water drop penetration time (WDPT) and the ethanol percentage (EP) tests. Sampling was conducted in the forest soils of two exotic species (Pinus pinaster, P, and Eucaliptus camaldulensis, E), used in the past for reforestation, and two native species (Quercus ilex, L, and Quercus pubescens, R). The WDPT vs. \u3b8 relationships exhibited a decreasing trend with a transition from hydrophobic to wettable conditions in the range \u3b8 = 0.14 - 0.19 cm3cm-3. The EP vs. \u3b8 relationships showed a maximum in the range \u3b8 = 0.10 - 0.15 cm3cm-3. Hydrophobicity in soils of native species persisted at relatively higher water content compared to exotic ones and it is expected to influence the hydrological processes to a greater extent

Assessing short- and long-term modifications of steady-state water infiltration rate in an extensive Mediterranean green roof

Green roof detention capacity is related to the steady-state infiltration rate, is, of the growing medium. With the aim to investigate short- and long-term modifications of the detention capacity of an extensive Mediterranean green roof, three mini-disk infiltrometer (MDI) measurement campaigns were conducted at construction, after one season and after five years of operation. A laboratory experiment was designed to separately measure is in the upper and the lower part of the substrate profile. During the first operating season, field is increased by a factor of 2.4 and 1.9 for near-saturated (applied pressure head, h0 = -30 mm) and quasi-saturated conditions (h0 = -5 mm), respectively. Similar rainfall height did not induce significant modifications in the upper layer of the laboratory columns, even if contribution of small pores to water infiltration tended to increase. Differently, is significantly decreased by a factor of 3.4-5.3 in the lower layer. After the simulated rainfall, the upper layer was less packed (mean bulk density, &amp; rho;b = 1.083 kg m-3) and the lower layer was more packed (&amp; rho;b = 1.218 kg m-3) as compared with the initial density (&amp; rho;b = 1.131 kg m-3) and the lower part enriched in small particles. Short-term modifications in the experimental plot were thus attributed to fine particles washing-off and bulk density decrease in the upper layer, yielding an overall more conductive porous medium. After five years of green roof operation, field is did not further increase thus showing that the washing/clogging mechanism was complete after one season or it was masked by counteracting processes, like root development and hydrophobicity