35,611 research outputs found
From ”Sapienza” to “Sapienza, State Archives in Rome”. A looping effect bringing back to the original source communication and culture by innovative and low cost 3D surveying, imaging systems and GIS applications
Applicazione di tecnologie mensorie integrate Low Cost,web GIS,applicazione di tecniche di Computational photography per la comunicazione e condivisione dei dati, sistemi di Cloud computing.Archiviazione Grandi DatiHigh Quality survey models, realized by multiple Low Cost methods and technologies, as a container to sharing Cultural and Archival Heritage, this is the aim guiding our research, here described in its primary applications. The SAPIENZA building, a XVI century masterpiece that represented the first unified headquarters of University in Rome, plays since year 1936, when the University moved to its newly edified campus, the role of the main venue for the State Archives. By the collaboration of a group of students of the Architecture Faculty, some integrated survey methods were applied on the monument with success. The beginning was the topographic survey, creating a reference on ground and along the monument for the upcoming applications, a GNNS RTK survey followed georeferencing points on the internal courtyard. Dense stereo matching photogrammetry is nowadays an accepted method for generating 3D survey models, accurate and scalable; it often substitutes 3D laser scanning for its low cost, so that it became our choice. Some 360°shots were planned for creating panoramic views of the double portico from the courtyard, plus additional single shots of some lateral spans and of pillars facing the court, as a single operation with a double finality: to create linked panotours with hotspots to web-linked databases, and 3D textured and georeferenced surface models, allowing to study the harmonic proportions of the classical architectural order. The use of free web Gis platforms, to load the work in Google Earth and the realization of low cost 3D prototypes of some representative parts, has been even performed
Bound States in Time-Dependent Quantum Transport: Oscillations and Memory Effects in Current and Density
The presence of bound states in a nanoscale electronic system attached to two
biased, macroscopic electrodes is shown to give rise to persistent,
non-decaying, localized current oscillations which can be much larger than the
steady part of the current. The amplitude of these oscillations depends on the
entire history of the applied potential. The bound-state contribution to the
{\em static} density is history-dependent as well. Moreover, the time-dependent
formulation leads to a natural definition of the bound-state occupations out of
equilibrium.Comment: 4 pages, 3 figure
The Effects of Clumps in Explaining X-ray Emission Lines from Hot Stars
It is now well established that stellar winds of hot stars are fragmentary
and that the X-ray emission from stellar winds has a strong contribution from
shocks in winds. Chandra high spectral resolution observations of line profiles
of O and B stars have shown numerous properties that had not been expected.
Here we suggest explanations by considering the X-rays as arising from bow
shocks that occur where the stellar wind impacts on spherical clumps in the
winds. We use an accurate and stable numerical hydrodynamical code to obtain
steady-state physical conditions for the temperature and density structure in a
bow shock. We use these solutions plus analytic approximations to interpret
some major X-ray features: the simple power-law distribution of the observed
emission measure derived from many hot star X-ray spectra and the wide range of
ionization stages that appear to be present in X-ray sources throughout the
winds. Also associated with the adiabatic cooling of the gas around a clump is
a significant transverse velocity for the hot plasma flow around the clumps,
and this can help to understand anomalies associated with observed line widths,
and the differences in widths seen in stars with high and low mass-loss rates.
The differences between bow shocks and the planar shocks that are often used
for hot stars are discussed. We introduce an ``on the shock'' (OTSh)
approximation that is useful for interpreting the X-rays and the consequences
of clumps in hot star winds and elsewhere in astronomy.Comment: to appear in the Astrophysical Journa
Numerical Experiments on the Two-step Emergence of Twisted Magnetic Flux Tubes in the Sun
We present the new results of the two-dimensional numerical experiments on
the cross-sectional evolution of a twisted magnetic flux tube rising from the
deeper solar convection zone (-20,000 km) to the corona through the surface.
The initial depth is ten times deeper than most of previous calculations
focusing on the flux emergence from the uppermost convection zone. We find that
the evolution is illustrated by the two-step process described below: the
initial tube rises due to its buoyancy, subject to aerodynamic drag due to the
external flow. Because of the azimuthal component of the magnetic field, the
tube maintains its coherency and does not deform to become a vortex roll pair.
When the flux tube approaches the photosphere and expands sufficiently, the
plasma on the rising tube accumulates to suppress the tube's emergence.
Therefore, the flux decelerates and extends horizontally beneath the surface.
This new finding owes to our large scale simulation calculating simultaneously
the dynamics within the interior as well as above the surface. As the magnetic
pressure gradient increases around the surface, magnetic buoyancy instability
is triggered locally and, as a result, the flux rises further into the solar
corona. We also find that the deceleration occurs at a higher altitude than in
our previous experiment using magnetic flux sheets (Toriumi and Yokoyama). By
conducting parametric studies, we investigate the conditions for the two-step
emergence of the rising flux tube: field strength > 1.5x10^4 G and the twist >
5.0x10^-4 km^-1 at -20,000 km depth.Comment: 42 pages, 13 figures, 2 tables, accepted for publication in ApJ.
High-resolution figures will appear in the published versio
Barrier and internal wave contributions to the quantum probability density and flux in light heavy-ion elastic scattering
We investigate the properties of the optical model wave function for light
heavy-ion systems where absorption is incomplete, such as Ca
and O around 30 MeV incident energy. Strong focusing effects
are predicted to occur well inside the nucleus, where the probability density
can reach values much higher than that of the incident wave. This focusing is
shown to be correlated with the presence at back angles of a strong enhancement
in the elastic cross section, the so-called ALAS (anomalous large angle
scattering) phenomenon; this is substantiated by calculations of the quantum
probability flux and of classical trajectories. To clarify this mechanism, we
decompose the scattering wave function and the associated probability flux into
their barrier and internal wave contributions within a fully quantal
calculation. Finally, a calculation of the divergence of the quantum flux shows
that when absorption is incomplete, the focal region gives a sizeable
contribution to nonelastic processes.Comment: 16 pages, 15 figures. RevTeX file. To appear in Phys. Rev. C. The
figures are only available via anonynous FTP on
ftp://umhsp02.umh.ac.be/pub/ftp_pnt/figscat
Isotope effect on the superfluid density in conventional and high-temperature superconductors
We investigate the isotope effect on the London penetration depth of a
superconductor which measures , the ratio of superfluid density to
effective mass. We use a simplified model of electrons weakly coupled to a
single phonon frequency , but assume that the energy gap
does not have any isotope effect. Nevertheless we find an isotope effect for
which is significant if is sufficiently large that it
becomes comparable to , a regime of interest to high cuprate
superconductors and possibly other families of unconventional superconductors
with relatively high . Our model is too simple to describe the cuprates
and it gives the wrong sign of the isotope effect when compared with
experiment, but it is a proof of principle that the isotope effect exists for
in materials where the pairing gap and is not of phonon origin
and has no isotope effect.Comment: 9 pages, 6 figure
Vortex Penetration into a Type II Superconductor due to a Mesoscopic External Current
Applying the London theory we study curved vortices produced by an external
current near and parallel to the surface of a type II superconductor. By
minimizing the energy functional we find the contour describing the hard core
of the flux line, and predict the threshold current for entrance of the first
vortex. We assume that the vortex entrance is allowed due to surface defects,
despite the Bean-Livingston barrier. Compared to the usual situation with a
homogeneous magnetic field, the main effect of the present geometry is that
larger magnetic fields can be applied locally before vortices enter the
superconducting sample. It is argued that this effect can be further enhanced
in anisotropic superconductors.Comment: 9 pages, 14 figure
Probing the Superfluid to Mott Insulator Transition at the Single Atom Level
Quantum gases in optical lattices offer an opportunity to experimentally
realize and explore condensed matter models in a clean, tunable system. We
investigate the Bose-Hubbard model on a microscopic level using single
atom-single lattice site imaging; our technique enables space- and
time-resolved characterization of the number statistics across the
superfluid-Mott insulator quantum phase transition. Site-resolved probing of
fluctuations provides us with a sensitive local thermometer, allows us to
identify microscopic heterostructures of low entropy Mott domains, and enables
us to measure local quantum dynamics, revealing surprisingly fast transition
timescales. Our results may serve as a benchmark for theoretical studies of
quantum dynamics, and may guide the engineering of low entropy phases in a
lattice
Object Classification in Astronomical Multi-Color Surveys
We present a photometric method for identifying stars, galaxies and quasars
in multi-color surveys, which uses a library of >65000 color templates. The
method aims for extracting the information content of object colors in a
statistically correct way and performs a classification as well as a redshift
estimation for galaxies and quasars in a unified approach. For the redshift
estimation, we use an advanced version of the MEV estimator which determines
the redshift error from the redshift dependent probability density function.
The method was originally developed for the CADIS survey, where we checked
its performance by spectroscopy. The method provides high reliability (6 errors
among 151 objects with R<24), especially for quasar selection, and redshifts
accurate within sigma ~ 0.03 for galaxies and sigma ~ 0.1 for quasars.
We compare a few model surveys using the same telescope time but different
sets of broad-band and medium-band filters. Their performance is investigated
by Monte-Carlo simulations as well as by analytic evaluation in terms of
classification and redshift estimation. In practice, medium-band surveys show
superior performance. Finally, we discuss the relevance of color calibration
and derive important conclusions for the issues of library design and choice of
filters. The calibration accuracy poses strong constraints on an accurate
classification, and is most critical for surveys with few, broad and deeply
exposed filters, but less severe for many, narrow and less deep filters.Comment: 21 pages including 10 figures. Accepted for publication in Astronomy
& Astrophysic
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