1,208 research outputs found
Computer Vision Tools for 3D Modelling in Archaeology
In archaeological Cultural Heritage study 3D modelling has become a very useful process to obtain indispensable data for documentation and visualization. Nowadays the continuous request to achieve photorealistic 3D models has led to testing different techniques and methodologies to speed up both data acquisition and the data processing phase. There are many examples of surveys conducted with the use of range-based and image-based techniques, but, in the last few years, the scientific research has been increasingly moving towards automatic procedures using Computer Vision approach to reduce time during data processing. Computer Vision approach offers a great opportunity for archaeological survey since it can be very easily used by existing Computer Vision interfaces such as 3D web services and open source or low cost software. The aim of this work is to evaluate the performance offered by Computer Vision interfaces for 3D survey of archaeological ruins using some 3D web-service tools and a low cost software like PhotoScan package. Some tests have been performed to analyze the geometric accuracy of 3D models obtained by 3D web-service tools and PhotoScan package through the comparison with a 3D model achieved by laser scanning survey.Dept. of Civil, Environmental, Aerospace and Materials Engineering, University of Palermo, Viale delle Scienze, 90128 Palermo, Ital
Cosmic Rays X. The cosmic ray knee and beyond: Diffusive acceleration at oblique shocks
Our purpose is to evaluate the rate of the maximum energy and the
acceleration rate that cosmic rays acquire in the non-relativistic diffusive
shock acceleration as it could apply during their lifetime in various
astrophysical sites, where highly oblique shocks exist. We examine numerically
(using Monte Carlo simulations) the effect of the diffusion coefficients on the
energy gain and the acceleration rate, by testing the role between the
obliquity of the magnetic field to the shock normal, and the significance of
both perpendicular cross-field diffusion and parallel diffusion coefficients to
the acceleration rate. We find (and justify previous analytical work - Jokipii
1987) that in highly oblique shocks the smaller the perpendicular diffusion
gets compared to the parallel diffusion coefficient values, the greater the
energy gain of the cosmic rays to be obtained. An explanation of the cosmic ray
spectrum in high energies, between eV and about eV is
claimed, as we estimate the upper limit of energy that cosmic rays could gain
in plausible astrophysical regimes; interpreted by the scenario of cosmic rays
which are injected by three different kind of sources, (a) supernovae which
explode into the interstellar medium, (b) Red Supergiants, and (c) Wolf-Rayet
stars, where the two latter explode into their pre-supernovae winds.Comment: Accepted in Astronomy and Astrophysics, 9 pages, 8 figures (for the
'Cosmic Rays' series papers
Improving Rigid 3-D Calibration for Robotic Surgery
Autonomy is the next frontier of research in robotic surgery and its aim is to improve the quality of surgical procedures in the next future. One fundamental requirement for autonomy is advanced perception capability through vision sensors. In this article, we propose a novel calibration technique for a surgical scenario with a da Vinci Research Kit (dVRK) robot. Camera and robotic arms calibration are necessary to precise position and emulate expert surgeon. The novel calibration technique is tailored for RGB-D cameras. Different tests performed on relevant use cases prove that we significantly improve precision and accuracy with respect to state of the art solutions for similar devices on a surgical-size setups. Moreover, our calibration method can be easily extended to standard surgical endoscope used in real surgical scenario
A landscape approach in the isotopic modeling of natural precipitations: two cases in Mediterranean mountain areas
The present paper proposes a method to simplify the very complex isotopic fractionation processes occurring during the water cycle. The method is constrained by a relatively small number of variables, with the precision needed in hydrological applications. After a theoretical
introduction on the adopted interpolation criteria, two cases in the Mediterranean are presented.
In both cases the evaluation of the âgeometric
complexityâ of the systems appears to be the
best tool to produce reliable isotopic models. If
the complexity is low, it is apparently easier to
fit different models; on the contrary the higher
the complexity is, more difficult it is to find a
reliable model but, at the same time, more difficult it is to find effective alternative models
Magnetic Field Generation in Core-Sheath Jets via the Kinetic Kelvin-Helmholtz Instability
We have investigated magnetic field generation in velocity shears via the
kinetic Kelvin-Helmholtz instability (kKHI) using a relativistic plasma jet
core and stationary plasma sheath. Our three-dimensional particle-in-cell
simulations consider plasma jet cores with Lorentz factors of 1.5, 5, and 15
for both electron-proton and electron-positron plasmas. For electron-proton
plasmas we find generation of strong large-scale DC currents and magnetic
fields which extend over the entire shear-surface and reach thicknesses of a
few tens of electron skin depths. For electron-positron plasmas we find
generation of alternating currents and magnetic fields. Jet and sheath plasmas
are accelerated across the shear surface in the strong magnetic fields
generated by the kKHI. The mixing of jet and sheath plasmas generates
transverse structure similar to that produced by the Weibel instability.Comment: 28 pages, 12 figures, in press, ApJ, September 10, 201
Value of epidermal growth factor receptor status compared with growth fraction and other factors for prognosis in early breast cancer.
The epidermal growth factor receptor (EGFR) is a transmembrane glycoprotein whose expression is important in the regulation of breast cancer cell growth. The relationship between EGFR status (determined by an immunocytochemical assay) and various prognostic factors was investigated in 164 primary breast cancers. Overall 56% of tumours were EGFR-positive and the expression of EGFR was unrelated to axillary node status, tumour size and histological grade; and it was poorly associated with the tumour proliferative activity measured by Ki-67 immuno-cytochemistry. The relapse-free survival (RFS) probability at 3-years was significantly worse for patients with EGFR positive tumours (P = 0.003) and for those whose Ki-67 score was > 7.5% (P = 0.0027), as well as in patients with axillary node involvement (P = 0.01) and with poorly differentiated tumours (P = 0.04). Immunocytochemical determination of EGFR and cell kinetics gave superimposable prognostic information for predicting RFS with odds ratios of 3.51, when evaluated singly. In our series of patients EGFR, Ki-67 and node status retain their prognostic value concerning RFS in multivariate analysis. The 3-year probability of overall survival (OS) was significantly better in node-negative patients (P = 0.04) and was similar in EGFR-positive and negative patients. In conclusion, EGFR status appears to be a significant and independent indicator of recurrence in human breast cancer and the concomitant measurement of the tumour proliferative activity seems to improve the selection of patients with different risks of recurrence
Active Galactic Nuclei Jets and Multiple Oblique Shock Acceleration: Starved Spectra
Shocks in jets and hot spots of Active Galactic Nuclei (AGN) are one
prominent class of possible sources of very high energy cosmic ray particles
(above 10^18eV). Extrapolating their spectrum to their plausible injection
energy from some shock, implies an enormous hidden energy for a spectrum of
index ~-2. Some analyzes suggest the particles' injection spectrum at source to
be as steep as -2.4 to -2.7, making the problem much worse, by a factor of
order 10^6. Nevertheless, it seems implausible that more than at the very best
1/3 of the jet energy, goes into the required flux of energetic particles thus,
one would need to allow for the possibility that there is an energy problem,
which we would like to address in this work. Sequences of consecutive oblique
shock features, or conical shocks, have been theorized and eventually observed
in many AGN jets. Based on that, we use by analogy the 'Comptonisation' effect
and we propose a scenario of a single injection of particles which are
accelerated consecutively by several oblique shocks along the axis of an AGN
jet. We use detailed test-particle approximation Monte Carlo simulations in
order to calculate particle spectra by acceleration at such a shock pattern
while monitoring the efficiency of acceleration, calculating differential
spectra. We find that the first shock of a sequence of oblique shocks,
establishes a low energy power-law spectrum with ~E^-2.7. The consecutive
shocks push the spectrum up in energy, rendering flatter distributions with
steep cut-offs and characteristic depletion at low energies, an effect which
could explain the puzzling apparent extra source power as well as the flat or
inverted spectra from distant flaring sources.Comment: 14 pages, submitted to A&
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