1,083 research outputs found
Redshift-Space Distortions and the Real-Space Clustering of Different Galaxy Types
We study the distortions induced by peculiar velocities on the redshift-space
correlation function of galaxies of different morphological types in the
Pisces-Perseus redshift survey. Redshift-space distortions affect early- and
late-type galaxies in different ways. In particular, at small separations, the
dominant effect comes from virialized cluster cores, where ellipticals are the
dominant population. The net result is that a meaningful comparison of the
clustering strength of different morphological types can be performed only in
real space, i.e., after projecting out the redshift distortions on the
two-point correlation function xi(r_p,pi). A power-law fit to the projected
function w_p(r_p) on scales smaller than 10/h Mpc gives r_o =
8.35_{-0.76}^{+0.75} /h Mpc, \gamma = 2.05_{-0.08}^{+0.10} for the early-type
population, and r_o = 5.55_{-0.45}^{+0.40} /h Mpc, \gamma =
1.73_{-0.08}^{+0.07} for spirals and irregulars. These values are derived for a
sample luminosity brighter than M_{Zw} = -19.5. We detect a 25% increase of r_o
with luminosity for all types combined, from M_{Zw} = -19 to -20. In the
framework of a simple stable-clustering model for the mean streaming of pairs,
we estimate sigma_12(1), the one-dimensional pairwise velocity dispersion
between 0 and 1 /h Mpc, to be 865^{+250}_{-165} km/s for early-type galaxies
and 345^{+95}_{-65} km/s for late types. This latter value should be a fair
estimate of the pairwise dispersion for ``field'' galaxies; it is stable with
respect to the presence or absence of clusters in the sample, and is consistent
with the values found for non-cluster galaxies and IRAS galaxies at similar
separations.Comment: 17 LaTeX pages including 3 tables, plus 11 PS figures. Uses AASTeX
macro package (aaspp4.sty) and epsf.sty. To appear on ApJ, 489, Nov 199
Infiltration Measurements for Soil Hydraulic Characterization
This book summarises the main results of many contributions from researchers worldwide who have used the water infiltration process to characterize soil in the field. Determining soil hydrodynamic properties is essential to interpret and simulate the hydrological processes of economic and environmental interest. This book can be used as a guide to soil hydraulic characterization and in addition it gives a complete description of the treated techniques, including an outline of the most significant research results, with the main points that still needing development and improvement
Failure envelopes of pile groups under inclined and eccentric load
A novel numerical procedure for defining failure envelopes of pile groups under inclined and eccentric load is proposed. The starting point is a closed-form exact solution for interaction diagram of pile groups under combined axial-moment loading recently published in the literature. Failure envelopes in the generalised force space are then derived as an extension of this solution by means of an incremental algorithm. It is shown that the axial load at foundation level has always a beneficial effect on the lateral capacity of the pile group, even if this favourable effect is often neglected in practice. On the contrary, the amount of interaction between the horizontal and moment components of the resultant action at failure is usually very small, with the exception of piles groups with end-bearing piles. Some example applications of the proposed method are provided and a simple, yet reliable procedure for ultimate limit-state analysis of pile groups subjected to inclined and eccentric loads is suggested
Osservazione e modellazione del deflusso sottosuperficiale laterale saturo in un ripido versante naturale
I versanti sono unità morfologiche fondamentali che governano la risposta idrologica
dei bacini idrografici durante le precipitazioni più intense. Nonostante la loro
riconosciuta importanza idrologica, è ancora necessario condurre approfonditi studi,
sia a carattere sperimentale che teoretico, per meglio comprendere i meccanismi di
generazione e trasporto del deflusso sottosuperficiale laterale saturo nei versanti. In
questo contributo sono presentati i risultati di un monitoraggio di lungo periodo del
flusso laterale di falda intercettato per mezzo di una trincea drenante installata su
d’un ripido versante naturale nel bacino del Lago di Baratz, Sardegna. I dati raccolti
vengono utilizzati per sviluppare una relazione di tipo esponenziale tra la conducibilitÃ
idraulica laterale satura (KS) e lo spessore della falda (T), valida alla scala di
versante. I flussi osservati e i livelli di falda sono simulati con un modello numerico
orizzontale 1D, basato sulla soluzione simultanea della legge del moto e dell’equazione
di bilancio idrico, e implementato tramite uno schema risolutivo alle differenza
finite. Le principali assunzioni del modello sono che nel suolo il flusso sottosuperficiale
saturo sia regolato dalla legge di Darcy, e che si verifichi sempre l’istantaneo
raggiungimento di un profilo di equilibrio idrostatico del carico di suzione nella
zona vadosa. Il modello richiede la specifica della curva di ritenzione idrica del
suolo e della relazione KS(T) ottenute sperimentalmente. I risultati della simulazione
indicano che il modello è in grado di riprodurre in modo adeguato i dati osservati. Il
flusso di falda è ben riprodotto, sia in termini di tempi di risposta che di portate drenate.
Pertanto, il modello sviluppato può essere un utile strumento di previsione
della risposta idrologica in versanti naturali a forte pendenza
The ESO Key-Programme ``A Homogeneous Bright QSO Survey'' - I The Methods and the ``Deep'' Fields
This is the first paper in a series aimed at defining a statistically
significant sample of QSOs in the range and .
The selection is carried out using direct plates obtained at the ESO and UK
Schmidt Telescopes, scanned with the COSMOS facility and searched for objects
with an ultraviolet excess. Follow-up spectroscopy, carried out at ESO La
Silla, is used to classify each candidate. In this initial paper, we describe
the scientific objectives of the survey; the selection and observing techniques
used. We present the first sample of 285 QSOs () in a 153 deg
area, covered by the six ``deep'' fields, intended to obtain significant
statistics down with unprecedented photometric accuracy. From
this database, QSO counts are determined in the magnitude range .Comment: 21 pages uuencoded compressed postscript, to appear in Astronomy and
Astrophysics Supplements, 199
SCHEMA SPERIMENTALE PER LA STIMA DELLA CONDUCIBILITÀ IDRAULICA LATERALE ALLA SCALA DI VERSANTE
La conducibilità idraulica alla saturazione, KS, è un parametro fondamentale per
la simulazione del flusso idrico nel suolo. La memoria illustra un approccio sperimentale
per la stima della KS laterale alla scala di versante. La metodologia proposta
è stata applicata in due aree contigue ricoperte, rispettivamente, da macchia mediterranea
e prato. Sono stati registrati i livelli di falda e i deflussi idrici sottosuperficiali,
e queste misure sono state usate per il calcolo della KS del suolo tramite l’equazione
di Darcy. Il monitoraggio è stato effettuato durante il periodo piovoso compreso tra
gennaio e giugno 2014. In aprile, inoltre, sono state eseguite prove di pioggia artificiale
con intensità di 30 e 70 mm h-1. Durante le precipitazioni naturali, il valore massimo
di KS stimato nel prato è stato di 2870 mm h-1, mentre è stato pari a 2400 mm h-1
nel corso delle prove di saturazione artificiale. Il valore massimo di KS pari 4000 mm
h-1 è stato ottenuto, nella macchia, durante le prove di pioggia artificiale. Per contro,
valori minori di KS sono stati ottenuti durante le piogge naturali a causa delle basse
portate sottosuperficiali registrate. La metodologia proposta è risultata idonea per la
stima di valori della conducibilità idraulica rappresentativi per le aree di interesse.
Tali informazioni potranno garantire una maggiore attendibilità della modellizzazione
dei processi idrologici a scala di versante e di bacino
Large-scale lateral saturated soil hydraulic conductivity as a metric for the connectivity of subsurface flow paths at hillslope scale
Lateral saturated soil hydraulic conductivity, Ks,l, is the soil property governing subsurface water transfer in hillslopes, and the key parameter in many numerical models simulating hydrological processes at the hillslope and catchment scales. Likewise, the hydrological connectivity of the lateral flow paths plays a significant role in determining the rate of the subsurface flow at various spatial scales. This study investigates the relationship between Ks,l and hydrological connectivity at the hillslope spatial scale. Ks,l was determined by the subsurface flow rates intercepted by drains and water table depths observed in a well network. The hydrological connectivity was evaluated by the synchronicity among water table peaks, and between these and the peaks of the drained flow. Rainfall and soil moisture were used to investigate the influence of the transient hydrological soil condition on connectivity and Ks,l. As the synchronicity of the water table response between wells increased, the lag times between the peaks of water levels and those of the drained subsurface flow decreased. Moreover, the most synchronic water table rises determined the highest drainage rates. The relationships between Ks,l and water table depths were highly non-linear, with a sharp increase in the values for water table levels close to the soil surface. Estimated Ks,l values for the full saturated soil were in the order of thousands of mm h−1, suggesting the activation of macropores in the root zone. The Ks,l values determined at the peak of the drainage events were correlated with the indicators of synchronicity. The sum of cumulative rainfall and antecedent soil moisture was correlated with the connectivity indicators and Ks,l. We suggest that, for simulating realistic processes at the hillslope scale, the hydrological connectivity could be implicitly considered in hydrological modelling through an evaluation of Ks,l at the same spatial scale
Seeking the Local Convergence Depth. V. Tully-Fisher Peculiar Velocities for 52 Abell Clusters
We have obtained I band Tully-Fisher (TF) measurements for 522 late-type
galaxies in the fields of 52 rich Abell clusters distributed throughout the sky
between 50 and 200\h Mpc. Here we estimate corrections to the data for various
forms of observational bias, most notably Malmquist and cluster population
incompleteness bias. The bias-corrected data are applied to the construction of
an I band TF template, resulting in a relation with a dispersion of 0.38
magnitudes and a kinematical zero-point accurate to 0.02 magnitudes. This
represents the most accurate TF template relation currently available.
Individual cluster TF relations are referred to the average template relation
to compute cluster peculiar motions. The line-of-sight dispersion in the
peculiar motions is 341+/-93 km/s, in general agreement with that found for the
cluster sample of Giovanelli and coworkers.Comment: 31 pages, 14 figures, uses AAS LaTeX; to appear in the Astronomical
Journa
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