1,431 research outputs found
New discoveries with geophysics in the Accademia of Hadrian's Villa near Tivoli (Rome)
The Accademia Pilot Project concerns one of the lesser known buildings of
Hadrian's Villa, the Accademia, which is still in private property and is
not open to the public. One of the most significant and unique features of
this building – and of the whole Villa – is a network of subterranean
service corridors, which was seldom studied.
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For the first time we used Geophysics at Hadrian's Villa, to explore the
subterranean tunnels of the Accademia and reconstruct their layout. The
survey was done by archaeologist Anna Maria Marras for her Master thesis in
Geo-technology (Marras, 2008) and gave very interesting results
Angular Correlations of the X-Ray Background and Clustering of Extragalactic X-Ray Sources
The information content of the autocorrelation function (ACF) of intensity
fluctuations of the X-ray background (XRB) is analyzed. The tight upper limits
set by ROSAT deep survey data on the ACF at arcmin scales imply strong
constraints on clustering properties of X-ray sources at cosmological distances
and on their contribution to the soft XRB. If quasars have a clustering radius
r_0=12-20 Mpc (H_0=50), and their two point correlation function, is constant
in comoving coordinates as indicated by optical data, they cannot make up more
40-50% of the soft XRB (the maximum contribution may reach 80% in the case of
stable clustering, epsilon=0). Active Star-forming (ASF) galaxies clustered
like normal galaxies, with r_0=10-12 Mpc can yield up to 20% or up to 40% of
the soft XRB for epsilon=-1.2 or epsilon=0, respectively. The ACF on degree
scales essentially reflects the clustering properties of local sources and is
proportional to their volume emissivity. The upper limits on scales of a few
degrees imply that hard X-ray selected AGNs have r_0<25 Mpc if epsilon=0 or
r_0<20 Mpc if epsilon=-1.2. No significant constraints are set on clustering of
ASF galaxies, due to their low local volume emissivity. The possible signal on
scales >6 deg, if real, may be due to AGNs with r_0=20 Mpc; the contribution
from clusters of galaxies with r_0~50 Mpc is a factor 2 lower.Comment: ApJ, in press (20 July 1993); 28 pages, TeX, ASTRPD-93-2-0
Gain of 20q11.21 in human pluripotent stem cells impairs TGF-β-dependent neuroectodermal commitment
Gain of 20q11.21 is one of the most common recurrent genomic aberrations in human pluripotent stem cells. Although it is known that overexpression of the antiapoptotic gene Bcl-xL confers a survival advantage to the abnormal cells, their differentiation capacity has not been fully investigated. RNA sequencing of mutant and control hESC lines, and a line transgenically overexpressing Bcl-xL, shows that overexpression of Bcl-xL is sufficient to cause most transcriptional changes induced by the gain of 20q11.21. Moreover, the differentially expressed genes in mutant and Bcl-xL overexpressing lines are enriched for genes involved in TGF-beta- and SMAD-mediated signaling, and neuron differentiation. Finally, we show that this altered signaling has a dramatic negative effect on neuroectodermal differentiation, while the cells maintain their ability to differentiate to mesendoderm derivatives. These findings stress the importance of thorough genetic testing of the lines before their use in research or the clinic
Archaeoastronomy in ancient Helvetia: the theater, the temple and the city of Aventicum (Avenches)
This article presents our discovery of the astronomical orientation of the city of Aventicum, the capital of ancient Roman Helvetia, where the sacred complex formed by the Temple of the Cigognier and the Theater were oriented along the axis that links the sunset of the Summer Solstice and the sunrise of the Winter Solstice. Also the East and West doors of the city were astronomically oriented on the axis that links the sunrise of the Summer Solstice and the sunset of the Winter Solstice. On July 13th, 2017 I had the fortune to visit two extraordinary Roman sites in Switzerland, Avenches and Vallon, together with friend Cristiano Castelletti, a great scholar as well as an excellent journalist of the Swiss-Italian Radio. This article is dedicated to his memory, because unfortunately Cristiano passed away in 2017, leaving a great void for us all
The symbolic use of light in Hadrianic architecture and the 'Kiss of the Sun'
In this presentation we will discuss three Roman monuments of the times of Emperor Hadrian (117-138 AD): the Villa Adriana at Tivoli near Rome, the Mausoleum of Hadrian in Rome (now Castel Sant'Angelo) and finally the Pantheon (also in Rome). In all of them we see luminous phenomena which occur only in few set days during the year; they correspond to astronomical events such as the Solstices or other important dates of the Roman calendar. As we will see, this did not happen by chance and had a precise symbolic meaning. Also, we will explain why there are no written sources about Roman oriented buildings and their illuminations, producing an ancient and rare documentation: the description of the "Kiss of the Sun"
Filter design for the detection of compact sources based on the Neyman-Pearson detector
This paper considers the problem of compact source detection on a Gaussian
background in 1D. Two aspects of this problem are considered: the design of the
detector and the filtering of the data. Our detection scheme is based on local
maxima and it takes into account not only the amplitude but also the curvature
of the maxima. A Neyman-Pearson test is used to define the region of
acceptance, that is given by a sufficient linear detector that is independent
on the amplitude distribution of the sources. We study how detection can be
enhanced by means of linear filters with a scaling parameter and compare some
of them (the Mexican Hat wavelet, the matched and the scale-adaptive filters).
We introduce a new filter, that depends on two free parameters (biparametric
scale-adaptive filter). The value of these two parameters can be determined,
given the a priori pdf of the amplitudes of the sources, such that the filter
optimizes the performance of the detector in the sense that it gives the
maximum number of real detections once fixed the number density of spurious
sources. The combination of a detection scheme that includes information on the
curvature and a flexible filter that incorporates two free parameters (one of
them a scaling) improves significantly the number of detections in some
interesting cases. In particular, for the case of weak sources embedded in
white noise the improvement with respect to the standard matched filter is of
the order of 40%. Finally, an estimation of the amplitude of the source is
introduced and it is proven that such an estimator is unbiased and it has
maximum efficiency. We perform numerical simulations to test these theoretical
ideas and conclude that the results of the simulations agree with the
analytical ones.Comment: 15 pages, 13 figures, version accepted for publication in MNRAS.
Corrected typos in Tab.
Mid- and Far-infrared Luminosity Functions and Galaxy Evolution from Multiwavelength Spitzer Observations up to z~2.5
[Abridged]We exploit a large homogeneous dataset to derive a self-consistent
picture of IR emission based on the time-dependent 24, 15, 12 and 8micron
monochromatic and bolometric IR luminosity functions (LF) over the 0<z<2.5
redshift range. Our analysis is based on the combination of data from deep
Spitzer surveys in the VVDS-SWIRE and GOODS areas. To our limiting flux of
S(24)=400microJy our derived sample in VVDS-SWIRE includes 1494 sources, and
666 and 904 sources brighter than S(24)=80microJy are catalogued in GOODS-S and
GOODS-N, respectively, for a total area of ~0.9 square degs. We obtain reliable
optical identifications and redshifts, providing us a rich and robust dataset
for our luminosity function determination. Based on the multi-wavelength
information available, we constrain the LFs at 8, 12, 15 and 24micron. We also
extrapolate total IR luminosities from our best-fit to the observed SEDs of
each source, and use this to derive the bolometric LF and comoving volume
emissivity up to z~2.5. In the 0<z<1 interval, the bolometric IR luminosity
density evolves as (1+z)^3.8+/-0.4. Although more uncertain at higher-z, our
results show a flattening of the IR luminosity density at z>1. The mean
redshift of the peak in the source number density shifts with luminosity: the
brighest IR galaxies appear to be forming stars earlier in cosmic time (z>1.5),
while the less luminous ones keep doing it at more recent epochs (z~1 for
L(IR)<10^11L_sun). Our results suggest a rapid increase of the galaxy IR
comoving volume emissivity back to z~1 and a constant average emissivity at
z>1. We also seem to find a difference in the evolution rate of the source
number densities as a function of luminosity, a downsizing evolutionary pattern
similar to that reported from other samples of cosmic sources.Comment: Accepted for pubblicantion in Astronomy and Astrophysic
Unveiling the oldest and most massive galaxies at very high redshift
(Abridged) This work explores the existence of high redshift massive galaxies
unveiled with Spitzer+IRAC, but missed by conventional selection techniques
based on optical and near-infrared observations. To this end, we use the
multi-wavelength imaging data available for the GOODS-South field, and select a
flux-limited sample from the IRAC 3.6um image to m(AB)<23.26. We confine our
study to the galaxies undetected by the optical HST+ACS imaging and close to
the detection limit of the K-band image (K>23.5 AB). Our selection unveiled 20
galaxies on which we performed a detailed photometric analysis. For each
galaxy, we built an SED based on optical-to-8um photometry to estimate the
photo-z and to derive the main galaxies physical properties. The majority of
the sample sources show degenerate/bimodal solutions for the photometric
redshifts (Abridged). These can either be heavily dust-enshrouded (Av~2-4)
starbursts at 210^12 Lsun, or massive
post-starburst galaxies in the redshift interval 4<z<9 with stellar masses of
10^11 Msun. One galaxy, the only source in our sample with both an X-ray and a
24um detection, might be an extremely massive object at z~8 detected during a
post-starburst phase with concomitant QSO activity (although a lower-z solution
is not excluded). Our investigation of Spitzer-selected galaxies with very red
SEDs and completely undetected in the optical reveals a potential population of
massive galaxies at z>4 which appear to include significant AGN emissions.
These sources may be the oldest stellar systems at z~4. These, previously
unrecognized, optically obscured objects might provide an important
contribution to the massive-end (M>10^11 sun) of the high-z stellar mass
function and they would almost double it (Abridged).Comment: Accepted for publication in Astronomy and Astrophysic
Endoscopic endonasal anatomy of superior orbital fissure and orbital apex regions: critical considerations for clinical applications.
An XMM-Newton Study of the Hard X-ray Sky
We report on the spectral properties of a sample of 90 hard X-ray selected
serendipitous sources detected in 12 XMM observations with 1<F(2-10)<80
10^(-14) erg/cm2/s. Approximately 40% of the sources are optically identified
with 0.1<z<2 and most of them are classified as broad line AGNs. A simple model
consisting of power law modified by Galactic absorption offers an acceptable
fit to ~65% of the source spectra. This fit yields an average photon index of
~1.55 over the whole sample. We also find that the mean slope of the
QSOs in our sample turns out to remain nearly constant (~1.8-1.9)
between 0<z<2, with no hints of particular trends emerging along z. An
additional cold absorption component with 10^(21)<Nh<10^(23) cm^(-2) is
required in ~30% of the sources. Considering only subsamples that are complete
in flux, we find that the observed fraction of absorbed sources (i.e. with
Nh>~10^(22) cm^(-2)) is ~30%, with little evolution in the range 2<F(2-10)<80
10^(-14) erg/cm2/s. Interestingly, this value is a factor ~2 lower than
predicted by the synthesis models of the CXB. This finding, detected for the
first time in this survey, therefore suggests that most of the heavily obscured
objects which make up the bulk of the CXB will be found at lower fluxes
(F(2-10)< 10^(-14) erg/cm2/s). This mismatch together with other recent
observational evidences which contrast with CXB model predictions suggest that
one (or more) of the assumptions usually included in these models need to be
revised.Comment: 20 pages, 13 figures, accepted for publication in A&
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