13,510 research outputs found
A novel system architecture for real-time low-level vision
A novel system architecture that exploits the spatial locality in memory access that is found in most low-level vision algorithms is presented. A real-time feature selection system is used to exemplify the underlying ideas, and an implementation based on commercially available Field Programmable Gate Arrays (FPGAâs) and synchronous SRAM memory devices is proposed. The peak memory access rate of a system based on this architecture is estimated at 2.88 G-Bytes/s, which represents a four to five times improvement with respect to existing reconfigurable computers
Characterization of classical Gaussian processes using quantum probes
We address the use of a single qubit as a quantum probe to characterize the
properties of classical noise. In particular, we focus on the characterization
of classical noise arising from the interaction with a stochastic field
described by Gaussian processes. The tools of quantum estimation theory allow
us to find the optimal state preparation for the probe, the optimal interaction
time with the external noise, and the optimal measurement to effectively
extract information on the noise parameter. We also perform a set of simulated
experiments to assess the performances of maximum likelihood estimator, showing
that the asymptotic regime, where the estimator is unbiased and efficient, is
approximately achieved after few thousands repeated measurements on the probe
system.Comment: 7 pages, 4 figures, to appear in Phys. Lett.
Microcracking in piezoelectric materials by the Boundary Element Method
A 3D boundary element model for piezoelectric polycrystalline micro-cracking is discussed in this contribution. The model is based on the boundary integral representation of the electro-mechanical behavior of individual grains and on the use of a generalized cohesive formulation for inter-granular micro-cracking. The boundary integral formulation allows to address the electro-mechanical boundary value problem in terms of generalized grain boundary and inter-granular displacements and tractions only, which implies the natural inclusion of the cohesive laws in the formulation, the simplification of the analysis pre-processing stage, and the reduction of the number of degrees of freedom of the overall analysis with respect to other popular numerical methods
Continuous-time quantum walks on dynamical percolation graphs
We address continuous-time quantum walks on graphs in the presence of time-
and space-dependent noise. Noise is modeled as generalized dynamical
percolation, i.e. classical time-dependent fluctuations affecting the tunneling
amplitudes of the walker. In order to illustrate the general features of the
model, we review recent results on two paradigmatic examples: the dynamics of
quantum walks on the line and the effects of noise on the performances of
quantum spatial search on the complete and the star graph. We also discuss
future perspectives, including extension to many-particle quantum walk, to
noise model for on-site energies and to the analysis of different noise
spectra. Finally, we address the use of quantum walks as a quantum probe to
characterize defects and perturbations occurring in complex, classical and
quantum, networks.Comment: 7 pages, 4 figures. Accepted for publication in EPL Perspective
Use of natural resins in repairing damaged timber beams â An experimental investigation
Different techniques including the application of steel elements, composite materials and polymeric resins have been used in the past to repair damaged timber beams. However, there is a growing need to replace these materials with those with minimal environmental impact. In addition, stringent requirements of conservation authorities on the compatibility between repair and parent materials have also necessitated search for innovative repair materials for timber beams. Therefore, an increasing shift of focus towards the use of materials derived from natural sources in repairing and reinforcing timber structures is currently experienced. This paper presents the results of an exploratory study on the use of natural resins (rosin and bone glue) in repairing oak timber beams. 15 oak timber beams with cross section dimensions of 67 x 67 mm and 1100 mm in length were tested in four-point bending to failure. Undamaged, damaged (unrepaired) and damaged but repaired timber beams (with rosin and bone glue) were tested. The effectiveness of the repair material and technique was analysed based on the bending capacity and mid span deflection at failure. The initial results show negligible effectiveness of rosin in repairing timber beams. In fact, about 16% reduction (average) in load carrying capacity with a corresponding 5% decrease (average) in maximum displacement was recorded. Relatively higher level of effectiveness was recorded with the use of bone glue (about 10 % average increase in load carrying capacity). However, over 30% corresponding average increase in the maximum displacement was also recorded. Further work investigating different repair techniques and other natural resins is presently underway
Towards an expanded model of litigation
Introduction: The call for contributions for this workshop describes the important new challenges for the legal search
community this domain brings. Rather than just understanding the challenges this domain poses in terms of
their technical properties, we would like to suggest that understanding these challenges as socio-technical
challenges will be important. That is, as well as calling for research on a technical level to address these
challenges we are also calling for work to understand the social practices of those involved in e-discovery
(ED) and related legal work. A particularly interesting feature of this field is that it is likely that search
technologies will (at least semi-)automate responsiveness review in the relatively near term and this will
change the way that the work is organised and done in many ways â offering new possibilities for new
ways of organising the work. As well as designing those technologies for automating responsiveness
review we need to be envisioning how the work will be done in the future, how these technologies will
impact the organisation of the case and so on. In this position paper we therefore outline the importance of
understanding the wider social context of ED when designing tools and technologies to support and change
the work. We would like to reinforce and expand on Conradâs call for IR researchers to understand just
what ED entails [2], include the stages that come both before and after core retrieval activities.
The importance of considering the social aspects of work in the design of the technology has been
established for some time. Ushering in this âturn to the social,â and focusing on interface design, Gentner
and Grudin [4] described how the GUI has already changed from an interface for engineers, representing
the engineering model of the machine to one that supported single âeverymanâ users (based on ideas from
psychology). From then onwards the interface has evolved to support groups of users, taking into account
the social and organisational contexts of use. This has particular resonance for the design of ED
technologies: during ED in particular and the wider legal process there are often many lawyers involved â
reviewing documents, determining issues, etc. Even if the way that their work is organised currently is not
seen as collaborative in the traditional sense â with individual lawyers working on individual document sets
to review them - their work needs to be coordinated and it seems likely that their work could be enhanced
by, for example, knowledge of what their colleagues had found, how the case was shaping up, new key
terms and facts turned up and so on. Work is often modelled for the purposes of design using process
models, but this misses out on the richness and variety actually found when one examines how the work is
carried out [3]. Technologies which strictly enforce the process models can often hinder the work, or end
up being worked around as was the case with workflow systems since people interpret processes very
flexibly to get the work done ([1], [3]). Other studies in other fields have found similar problems when
systems are designed on for example cognitive models of how the work is done; they often do not take into
account the situated nature of the work and thus they can be very difficult to use [5]. We believe, like [2],
that a clear understanding of the social practices of ED is vital for the creation of high-quality, meaningful
tools and technologies. We furthermore propose that work practice studies, to be used in combination with
other methods, are a central part of getting the detailed understanding of the work practices central to
designing useful and intelligent tools. Work practice studies would involve ethnographies, consisting
primarily of observation, undertaken of practitioners engaging in the work of ED
Characterization of qubit chains by Feynman probes
We address the characterization of qubit chains and assess the performances
of local measurements compared to those provided by Feynman probes, i.e.
nonlocal measurements realized by coupling a single qubit regis- ter to the
chain. We show that local measurements are suitable to estimate small values of
the coupling and that a Bayesian strategy may be successfully exploited to
achieve optimal precision. For larger values of the coupling Bayesian local
strategies do not lead to a consistent estimate. In this regime, Feynman probes
may be exploited to build a consistent Bayesian estimator that saturates the
Cram\'er-Rao bound, thus providing an effective characterization of the chain.
Finally, we show that ultimate bounds to precision, i.e. saturation of the
quantum Cram\'er-Rao bound, may be achieved by a two-step scheme employing
Feynman probes followed by local measurements.Comment: 8 pages, 5 figure
Dynamics of quantum correlations in colored environments
We address the dynamics of entanglement and quantum discord for two non
interacting qubits initially prepared in a maximally entangled state and then
subjected to a classical colored noise, i.e. coupled with an external
environment characterized by a noise spectrum of the form . More
specifically, we address systems where the Gaussian approximation fails, i.e.
the sole knowledge of the spectrum is not enough to determine the dynamics of
quantum correlations. We thus investigate the dynamics for two different
configurations of the environment: in the first case the noise spectrum is due
to the interaction of each qubit with a single bistable fluctuator with an
undetermined switching rate, whereas in the second case we consider a
collection of classical fluctuators with fixed switching rates. In both cases
we found analytical expressions for the time dependence of entanglement and
quantum discord, which may be also extended to a collection of flcutuators with
random switching rates. The environmental noise is introduced by means of
stochastic time-dependent terms in the Hamiltonian and this allows us to
describe the effects of both separate and common environments. We show that the
non-Gaussian character of the noise may lead to significant effects, e.g.
environments with the same power spectrum, but different configurations, give
raise to opposite behavior for the quantum correlations. In particular,
depending on the characteristics of the environmental noise considered, both
entanglement and discord display either a monotonic decay or the phenomena of
sudden death and revivals. Our results show that the microscopic structure of
environment, besides its noise spectrum, is relevant for the dynamics of
quantum correlations, and may be a valid starting point for the engineering of
non-Gaussian colored environments.Comment: 8 pages, 3 figure
Non-Markovian continuous-time quantum walks on lattices with dynamical noise
We address the dynamics of continuous-time quantum walks on one-dimensional
disordered lattices inducing dynamical noise in the system. Noise is described
as time-dependent fluctuations of the tunneling amplitudes between adjacent
sites, and attention is focused on non-Gaussian telegraph noise, going beyond
the usual assumption of fast Gaussian noise. We observe the emergence of two
different dynamical behaviors for the walker, corresponding to two opposite
noise regimes: slow noise (i.e. strong coupling with the environment) confines
the walker into few lattice nodes, while fast noise (weak coupling) induces a
transition between quantum and classical diffusion over the lattice. A phase
transition between the two dynamical regimes may be observed by tuning the
ratio between the autocorrelation time of the noise and the coupling between
the walker and the external environment generating the noise. We also address
the non-Markovianity of the quantum map by assessing its memory effects, as
well as evaluating the information backflow to the system. Our results suggest
that the non-Markovian character of the evolution is linked to the dynamical
behavior in the slow noise regime, and that fast noise induces a Markovian
dynamics for the walker.Comment: 10 pages, 8 figure
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