1,286 research outputs found
Crystallization of fractional charges in a strongly interacting quasi-helical quantum dot
The ground-state electron density of a one-dimensional spin-orbit coupled
quantum dot with a Zeeman term and strong electron interaction is studied at
the fractional helical liquid points. We show that at fractional filling
factors (with a non-negative integer) the density
oscillates with peak. For a number of peaks larger than
the number of electrons suggests that a crystal of fractional
quasi-particles with charge (with the electron charge) occurs. The
reported effect is amenable of verification via transport measurements in
charged AFM-coupled dot
Modellare lo scavo archeologico: esperienze e tecniche a confronto
By examining the potential offered by the digital survey, the article aims at encouragÂŹing archaeologists to undertake a more rational approach towards three-dimensional data acquisition and management. Data was derived from excavations at Aveia (AQ - Italy) and Seglamen (Ethiopia). The 3D data-capture was achieved with the laser scanner and structure from motion techniques that make it possible to obtain a point cloud of an object from a sequence of photographic images, which are neither ordered nor calibrated. The conclusions reflect the role of digital technologies in the field of stratigraphic survey. Independence from scale and the ability to extract profiles and contours of stratigraphic units are factors of great importance for a virtual reconstruction of archaeological excavations
Neural networks for gamma-hadron separation in MAGIC
Neural networks have proved to be versatile and robust for particle
separation in many experiments related to particle astrophysics. We apply these
techniques to separate gamma rays from hadrons for the MAGIC Cerenkov
Telescope. Two types of neural network architectures have been used for the
classi cation task: one is the MultiLayer Perceptron (MLP) based on supervised
learning, and the other is the Self-Organising Tree Algorithm (SOTA), which is
based on unsupervised learning. We propose a new architecture by combining
these two neural networks types to yield better and faster classi cation
results for our classi cation problem.Comment: 6 pages, 4 figures, to be published in the Proceedings of the 6th
International Symposium ''Frontiers of Fundamental and Computational
Physics'' (FFP6), Udine (Italy), Sep. 26-29, 200
Full Characterization of the First 1 Inch Industrial Prototype of a New Concept Photodetector
The VSiPMT (Vacuum Silicon PhotoMultiplier Tube) is an original design for an
innovative light detector we proposed with the aim to create new scientific
instrumentation for industrial applications and physics research. The idea
behind this device is to replace the classical dynode chain of a
photomultiplier tube with a silicon photomultiplier, the latter acting as an
electron detector and amplifier. The VSiPMT offers very attractive features and
unprecedented performance, definitely superior to every other photodetector
with comparable sensitive surface, such as: negligible power cosumption,
excellent photon counting, easy low-voltage-based stabilization and very good
time performance. After the feasibility test of the idea, Hamamatsu Photonics
realized for our research group two VSiPMT industrial prototypes, that have
been fully characterized. The results of the full characterization of the
1-inch industrial prototype are presented in this work.Comment: 11 pages, 14 figure
A 3D environment to rebuild virtually the so-called Augusteum in Herculaneum
Computer graphics and three-dimensional modelling techniques have extended the possibilities of archaeologists in the creation of virtual reconstruction of ancient sites and monuments. Modern computational systems allow the implementation of computer-generated scenarios tailored on human cognitive capacities. Although Virtual Archaeology is not a novelty in the panorama of archaeological methods, there is no agreement among scholars on the minimal parameters necessary to virtually rebuild an ancient context, nor is there any requirement needed to guarantee the accuracy and the effectiveness of the final reconstruction; the strength of a model is based mainly on the capacity of the archaeologist to check the final result in terms of comparison between interpretations and hypotheses. The paper aims at exploring how the archaeologists could perform their work in a computational laboratory thanks to shared 3D models. The case study selected is the recent virtual reconstruction of the so-called Basilica in Herculaneum, a monument - 250 years after its discovery - still largely unexplained. The building is completely buried by volcanic lava save for part of its entrance porch. It was extensively explored using tunnels and looted by its early excavators. Different scholars have rebuilt the monument mainly on the basis of two plans, drawn in the 18th century, and few notes taken by the archaeologists during the exploration. The 3D model, carried out by integrating cad modelling with close-range photogrammetry, is intended to highlight some controversial parts of the reconstructions. Metadata associated to the digital replica describe the physical object and register all phases from data-acquisition to data-visualization in order to allow the validation of the model and the use or re-use of the digital resource
Induced gravitational collapse at extreme cosmological distances: the case of GRB 090423
CONTEXT: The induced gravitational collapse (IGC) scenario has been
introduced in order to explain the most energetic gamma ray bursts (GRBs),
Eiso=10^{52}-10^{54}erg, associated with type Ib/c supernovae (SNe). It has led
to the concept of binary-driven hypernovae (BdHNe) originating in a tight
binary system composed by a FeCO core on the verge of a SN explosion and a
companion neutron star (NS). Their evolution is characterized by a rapid
sequence of events: [...]. AIMS: We investigate whether GRB 090423, one of the
farthest observed GRB at z=8.2, is a member of the BdHN family. METHODS: We
compare and contrast the spectra, the luminosity evolution and the
detectability in the observations by Swift of GRB 090423 with the corresponding
ones of the best known BdHN case, GRB 090618. RESULTS: Identification of
constant slope power-law behavior in the late X-ray emission of GRB 090423 and
its overlapping with the corresponding one in GRB 090618, measured in a common
rest frame, represents the main result of this article. This result represents
a very significant step on the way to using the scaling law properties, proven
in Episode 3 of this BdHN family, as a cosmological standard candle.
CONCLUSIONS: Having identified GRB 090423 as a member of the BdHN family, we
can conclude that SN events, leading to NS formation, can already occur already
at z=8.2, namely at 650 Myr after the Big Bang. It is then possible that these
BdHNe originate stem from 40-60 M_{\odot} binaries. They are probing the
Population II stars after the completion and possible disappearance of
Population III stars.Comment: 9 pages, 9 figures, to appear on A&
Supernova 2012ec: Identification of the progenitor and early monitoring with PESSTO
We present the identification of the progenitor of the Type IIP SN 2012ec in
archival pre-explosion HST WFPC2 and ACS/WFC F814W images. The properties of
the progenitor are further constrained by non-detections in pre-explosion WFPC2
F450W and F606W images. We report a series of early photometric and
spectroscopic observations of SN 2012ec. The r'-band light curve shows a
plateau with M(r')=-17.0. The early spectrum is similar to the Type IIP SN
1999em, with the expansion velocity measured at Halpha absorption minimum of
-11,700 km/s (at 1 day post-discovery). The photometric and spectroscopic
evolution of SN 2012ec shows it to be a Type IIP SN, discovered only a few days
post-explosion (<6d). We derive a luminosity for the progenitor, in comparison
with MARCS model SEDs, of log L/Lsun = 5.15+/-0.19, from which we infer an
initial mass range of 14-22Msun. This is the first SN with an identified
progenitor to be followed by the Public ESO Spectroscopic Survey of Transient
Objects (PESSTO).Comment: 6 pages, 3 figures, MNRAS accepte
Passive noise control oriented design of aircraft headrests
Two Passive Noise Control (PNC) concepts were numerically evaluated in terms of their impact on the Sound Pressure Level (SPL) perceived by passengers of an aircraft flight.
A concept was based on the shape optimization of the headrests, whereas the second one was based on the adoption of a high absorbing material, i.e. a nanofiber textile, to improve the acoustic performances of the headrests.
To this aim, an aircraft seat was modelled with the Boundary Element Method (BEM) and loaded with a spherical distribution of monopole sources surrounding the seat. Different configurations of headrest shape and covering textiles were then compared in terms of the SPL calculated at passengersâ ears.
The work shows how an acoustic-oriented design of the aircraft headrests could achieve an average SPL reduction for passengers up to 3 dBA
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