12,329 research outputs found
One-handed hammer-spanner for chucks
Modified spanner wrench with a heavy hammer-piece hinged to its handle allows one hand removal of a tool from a chuck
Dynamics of a particle confined in a two-dimensional dilating and deforming domain
Some recent results concerning a particle confined in a one-dimensional box
with moving walls are briefly reviewed. By exploiting the same techniques used
for the 1D problem, we investigate the behavior of a quantum particle confined
in a two-dimensional box (a 2D billiard) whose walls are moving, by recasting
the relevant mathematical problem with moving boundaries in the form of a
problem with fixed boundaries and time-dependent Hamiltonian. Changes of the
shape of the box are shown to be important, as it clearly emerges from the
comparison between the "pantographic", case (same shape of the box through all
the process) and the case with deformation.Comment: 13 pages, 2 figure
Nanoseismic monitoring for detection of rockfalls. Experiments in quarry areas
Le frane per crollo da ammassi rocciosi fratturati sono tra i processi di instabilità gravitativa che più frequentemente interessano opere antropiche quali tagli su versanti naturali o artificiali, pareti di cava, trincee stradali, autostradali o ferroviarie, sia per ciò che attiene le aree di distacco che per quelle di accumulo. Nell’ambito dell’applicazione di sistemi di early warning per la gestione del rischio geologico legato a queste tipologie di frana, una sperimentazione della tecnica del monitoraggio nanosismometrico è stata effettuata presso due siti estrattivi non più in attività : le “Pirrere” della Baia di Cala Rossa sull’isola di Favignana (Trapani), in Sicilia, e la cava dismessa di Acuto (Frosinone), in Italia Centrale. Il monitoraggio nanosismometrico è una tecnica di indagine che consente di individuare e localizzare deboli eventi sismici, fino a magnitudo locale (ML) nell’ordine di -3, attraverso l’impiego di quattro sensori sismometrici disposti secondo una specifica geometria di array detta SNS (Seismic Navigation System).
Nel presente lavoro, mediante il software NanoseismicSuite sono stati analizzati 73 eventi di crollo indotti artificialmente attraverso la caduta controllata di blocchi di roccia nei due siti estrattivi abbandonati; sono stati lanciati, simulando fenomeni di rockfalls, rispettivamente 47 blocchi di roccia nella cava di Acuto e 26 eventi in quattro diverse cave a cielo aperto presenti nel settore occidentale di Cala Rossa. Tali eventi, avendo punto epicentrale noto, hanno permesso di determinare il miglior modello di sottosuolo in termini di valori di velocità delle onde P ed S attraverso un’operazione di back analysis. L’analisi è stata, infatti, effettuata variando i valori di velocità e scegliendo quelli relativi all’epicentro teorico ottenuto dall’analisi dell’evento che fosse il più vicino possibile al punto reale di impatto del blocco di roccia. Al fine di valutare la sensibilità della geometria dell’array SNS e l’influenza del sito di installazione sulla capacità di individuare e localizzare gli eventi, le sperimentazioni sono state condotte sia variando il raggio di apertura che la zona di installazione degli array: presso Acuto le acquisizioni di segnale sono state condotte prima con un array SNS con apertura di 20 m e successivamente con un array di apertura 10 m, mentre presso Cala Rossa l’array è stato installato alternativamente all’aperto in un’area di plateau roccioso ed in una galleria facente parte dell’area di cava abbandonata.
Analizzando i dati si è ottenuta una precisione dell’ubicazione epicentrale compresa tra il 10 ed il 22% della distanza che intercorre tra la sorgente e l’array nanosismometrico. Il miglior modello di sottosuolo ottenuto per entrambi i casi di studio è risultato avere una velocità delle onde P pari a 900 m/s ed un rapporto VP/VS pari a 1.73, valori in accordo con le condizioni di intenso stato di fratturazione delle rocce carbonatiche affioranti nelle due zone di cava. Per gli eventi di crollo indotti la magnitudo ML è risultata essere compresa tra -2.8 e -1.3; considerando l’energia sviluppata dall’impatto, legata alla massa del blocco ed all’altezza e alla velocità di caduta, non è stato possibile definire una relazione tra magnitudo ed energia, probabilmente a causa delle differenti caratteristiche del punto di impatto dei diversi blocchi. In generale, si è osservato che la precisione di ubicazione degli eventi, in termini di azimuth e distanza dal reale epicentro, è risultata paragonabile sia variando l’apertura dell’array che variando il sito di installazione. Per il sito sperimentale di Acuto, il processo di picking manuale del tempo di primo arrivo delle onde P è risultato essere più affidabile nel caso di array con apertura pari a 10 m. La sperimentazione effettuata a Cala Rossa ha permesso, invece, di osservare una migliore capacità di individuazione degli eventi nelle tracce relative all’array posizionato in galleria a causa della minore rumorosità di base del sito di installazione.
Tra le registrazioni sismometriche sono state identificate varie tipologie di segnali, oltre a quelli generati dal lancio dei blocchi, alcune riconducibili ad eventi naturali di crollo altre a deboli terremoti. L’analisi dei segnali riferibili alla prima tipologia di eventi naturali, effettuata tenendo in considerazione i modelli di sottosuolo precedentemente calibrati, ha portato all’identificazione in ambedue i siti di aree aventi maggiore suscettibilità a frane per crollo. In definitiva, si può ritenere che i risultati ottenuti in questo studio siano incoraggianti rispetto all’efficacia della tecnica di monitoraggio nanosismometrico nell’individuazione e nell’ubicazione di fenomeni di crollo in roccia e portano a ritenere questa tecnica potenzialmente applicabile in aree in cui tali eventi possono interferire con infrastrutture antropiche.In the frame of early warning and risk mitigation studies for landslide processes involving rock masses, two quarry areas (Cala Rossa Bay in Sicily and Acuto in Central Italy) were monitored with SNS (Seismic Navigation System) arrays. In this study, 73 rockfalls were simulated by launches of rock blocks. This allowed to perform a back analysis for defining the best seismic velocity model of the subsoil half-space; the records related to each impact caused by the rock block launch were managed by the nanoseismic monitoring approach, varying the velocity model to obtain a theoretical epicentre as close as possible to the actual location of the impact point. In order to evaluate the sensibility of the SNS array, the results obtained by different array apertures and positions were compared in terms of azimuth and distance error with respect to the real epicentres. On the other hand, several natural rockfalls were detected; their analysis allowed to identify areas having higher susceptibility to rockfalls by using the previously calibrated subsoil half-space model. Further studies are required to better define the areas prone to rockfall generation in the considered test sites; nevertheless, the here obtained results show an encouraging perspective about the application of the nanoseismic monitoring with respect to vulnerable infrastructures in rockfall prone areas
Recorded displacements in a landslide slope due to regional and teleseismic earthquakes
Regional and teleseismic earthquakes can induce displacements along joints in a landslideinvolved
rocky slope in Central Italy. The rarity of these effects is due to specific physical
properties of the seismic signals associated with: (i) the energy content, (ii) the distribution of
relative energy and peak of ground acceleration related to the ground motion components and
(iii) the spectral amplitude distribution in the frequency domain; these properties allow the
triggering earthquakes to be distinguished from the others. The observed effects are relevant
when compared to the direction of the landslide movement and the dimensions of the involved
rock mass volume. The landslide movement is less constrained in the direction parallel to the
dip of the slope and the landslide dimensions are associated with characteristic periods that
control the landslide deformational response in relation to the spectral content of the ground
motion. The earthquake-induced displacements are significant because they have the same
order of magnitude as the average annual cumulative displacement based on a decade of strain
measurements within the slope
Experimental evidence of laser power oscillations induced by the relative Fresnel (Goos-Haenchen) phase
The amplification of the relative Fresnel (Goos-Haenchen) phase by an
appropriate number of total internal reflections and the choice of favorable
incidence angles allow to observe full oscillations in the power of a DPSS
laser transmitted through sequential BK7 blocks. The experimental results
confirm the theoretical predictions. The optical apparatus used in this letter
can be seen as a new type of two-phase ellipsometric system where the phase of
the complex refractive index is replaced by the relative Fresnel
(Goos-Haenchen) phase.Comment: 7 pages, 3 figures, 1 tabl
How does informational heterogeneity affect the quality of forecasts?
We investigate a toy model of inductive interacting agents aiming to forecast
a continuous, exogenous random variable E. Private information on E is spread
heterogeneously across agents. Herding turns out to be the preferred
forecasting mechanism when heterogeneity is maximal. However in such conditions
aggregating information efficiently is hard even in the presence of learning,
as the herding ratio rises significantly above the efficient-market expectation
of 1 and remarkably close to the empirically observed values. We also study how
different parameters (interaction range, learning rate, cost of information and
score memory) may affect this scenario and improve efficiency in the hard
phase.Comment: 11 pages, 5 figures, updated version (to appear in Physica A
Analysis of the seismic site effects along the ancient Via Laurentina (Rome)
This paper presents an evaluation of the Local Seismic Response (LSR)
along the route of the ancient Roman road Via Laurentina, which has
been exposed in several areas of southwest Rome over the last decade
during the construction of new buildings and infrastructures. It is
an example of LSR analysis applied to ancient and archaeological
sites located in alluvial valleys with some methodological inferences
for the design of infrastructure and urban planning. Since the ancient
road does not cross the alluvial valley (namely the Fosso di Vallerano
Valley) normal to its sides, it was not possible to directly perform
2D numerical modelling to evaluate the LSR along the road route.
Therefore, outputs of 2D numerical models, obtained along three cross
sections that were normal oriented respect to the valley, were projected
along the route of the Via Laurentina within a reliable buffer attributed
according to an available high-resolution geological model of the
local subsoil. The modelled amplification functions consider physical
effects due to both the 2D shape of the valley and the heterogeneities
of the alluvial deposits. The 1D and 2D amplification functions were
compared to output that non-negligible effects are related to the narrow
shape of the fluvial valley and the lateral contacts between the
lithotecnical units composing the alluvial fill. The here experienced
methodology is suitable for applications to the numerical modelling of
seismic response in case of linear infrastructures (i.e., roads, bridges,
railways) that do not cross the natural system along physically characteristic
directions (i.e. longitudinally or transversally)
DISPLACEMENTS OF AUTOMORPHISMS OF FREE GROUPS II: CONNECTIVITY OF LEVEL SETS AND DECISION PROBLEMS
This is the second of two papers in which we investigate the properties of
displacement functions of automorphisms of free groups (more generally, free products)
on the Culler-Vogtmann Outer space CVn and its simplicial bordification. We develop a
theory for both reducible and irreducible autormorphisms. As we reach the bordification
of CVn we have to deal with general deformation spaces, for this reason we developed
the theory in such generality. In our previous first paper we studied general properties of the
displacement functions, such as well-orderability of the spectrum and the topological
characterization of min-points via partial train tracks (possibly at infinity).
This paper is devoted to proving that for any automorphism (reducible or not) any
level set of the displacement function is connected. Here, by the “level set” we intend to
indicate the set of points displaced by at most some amount, rather than exactly some
amount; this is sometimes called a “sub-level set”.
As an application, this result provides a stopping procedure for brute force search
algorithms in CVn. We use this to reprove two known algorithmic results: the conjugacy
problem for irreducible automorphisms and detecting irreducibility of automorphisms
Superconductivity in ropes of carbon nanotubes
Recent experimental and theoretical results on intrinsic superconductivity in
ropes of single-wall carbon nanotubes are reviewed and compared. We find strong
experimental evidence for superconductivity when the distance between the
normal electrodes is large enough. This indicates the presence of attractive
phonon-mediated interactions in carbon nanotubes, which can even overcome the
repulsive Coulomb interactions. The effective low-energy theory of rope
superconductivity explains the experimental results on the
temperature-dependent resistance below the transition temperature in terms of
quantum phase slips. Quantitative agreement with only one fit parameter can be
obtained. Nanotube ropes thus represent superconductors in an extreme 1D limit
never explored before.Comment: 19 pages, 9 figures, to appear in special issue of Sol. State Com
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