Active Estimation of Distance in a Robotic Vision System that Replicates Human Eye Movement

Many visual cues, both binocular and monocular, provide 3D information. When an agent moves with respect to a scene, an important cue is the different motion of objects located at various distances. While a motion parallax is evident for large translations of the agent, in most head/eye systems a small parallax occurs also during rotations of the cameras. A similar parallax is present also in the human eye. During a relocation of gaze, the shift in the retinal projection of an object depends not only on the amplitude of the movement, but also on the distance of the object with respect to the observer. This study proposes a method for estimating distance on the basis of the parallax that emerges from rotations of a camera. A pan/tilt system specifically designed to reproduce the oculomotor parallax present in the human eye was used to replicate the oculomotor strategy by which humans scan visual scenes. We show that the oculomotor parallax provides accurate estimation of distance during sequences of eye movements. In a system that actively scans a visual scene, challenging tasks such as image segmentation and figure/ground segregation greatly benefit from this cue.National Science Foundation (BIC-0432104, CCF-0130851

A Theoretical Analysis of the Influence of Fixational Instability on the Development of Thalamocortical Connectivity

Under natural viewing conditions, the physiological inotability of visual fixation keeps the projection of the stimulus on the retina in constant motion. After eye opening, chronic exposure to a constantly moving retinal image might influence the experience-dependent refinement of cell response characteristics. The results of previous modeling studies have suggested a contribution of fixational instability in the Hebbian maturation of the receptive fields of V1 simple cells (Rucci, Edelman, & Wray, 2000; Rucci & Casile, 2004). This paper presents a mathematieal explanation of our previous computational results. Using quasi-linear models of LGN units and V1 simple cells, we derive analytical expressions for the second-order statistics of thalamocortical activity before and after eye opening. We show that in the presence of natural stimulation, fixational instability introduces a spatially uncorrelated signal in the retinal input, whieh strongly influences the structure of correlated activity in the model

Working with register in the classroom: the Spanish case

1nonenoneRUCCI M.Rucci, Marc

Molecular biology of bone remodelling

Bone remodelling is an active and dynamic process that relies on the correct balance between bone resorption by osteoclasts and bone deposition by osteoblasts. Moreover, these two functions must be tightly coupled not only quantitatively, but also in time and space. When the coupling is lost, the correct bone mass could be compromised, leading to several skeletal pathologies. Indeed, bone loss and osteoporosis are the result of an increased osteoclast function and/or a reduced osteoblast activity. In contrast, other pathologies are related to osteoclast failure to resorbe bone, such as osteopetrosis, a rare genetic disorder characterized by an increased bone mass and also linked to an impairment of bone marrow functions. Starting from these assumptions, it is necessary to more deeply understand the molecular mechanisms regulating bone cell functions. Indeed, recent studies evidenced a complex interplay between the immune and skeletal systems, which share several regulatory molecules including cytokines, receptors and transcription factors. These data allowed to more deeply understand the mechanisms underlying bone mass regulation and could open new avenue to identify target molecules for alterantive therapies more efficacious against bone diseases

Modeling the Possible Influences of Eye Movements on the Refinement of Cortical Direction Selectivity

The second-order statistics of neural activity was examined in a model of the cat LGN and V1 during free-viewing of natural images. In the model, the specific patterns of thalamocortical activity required for a Bebbian maturation of direction-selective cells in VI were found during the periods of visual fixation, when small eye movements occurred, but not when natural images were examined in the absence of fixational eye movements. In addition, simulations of stroboscopic reming that replicated the abnormal pattern of eye movements observed in kittens chronically exposed to stroboscopic illumination produced results consistent with the reported loss of direction selectivity and preservation of orientation selectivity. These results suggest the involvement of the oculomotor activity of visual fixation in the maturation of cortical direction selectivity

Heavy quarkonia in strong magnetic fields

We investigate the influence of a homogeneus and constant strong external magnetic field on the heavy-meson spectrum. Quarkonium states $c\bar{c}$ and $b\bar{b}$ are described within a non-relativistic framework and by means of a suitable potential model based on the Cornell parametrization. In particular, in this work we propose a model which takes into account the possible anisotropies emerging at the level of the static quark-antiquark potential, as observed in recent lattice studies. The investigation is perfomed both with and without taking into account the anisotropy of the static potential, in order to better clarify its effectsComment: 10 pages, 9 figures, 3 tables, minor changes, references adde

Delta nitrogen tetroxide fueling operations

The development of the Delta second stage nitrogen tetroxide fueling system is briefly summarized. The nitrogen tetroxide fueling system and the equipment used to protect the spacecraft environment from the toxic nitrogen tetroxide fumes are described. Topics covered include: the nitrogen tetroxide transfer system; loading operations; safety precautions; and chemical treatment of all toxic vapors

EyeRIS: A General-Purpose System for Eye Movement Contingent Display Control

In experimental studies of visual performance, the need often emerges to modify the stimulus according to the eye movements perfonncd by the subject. The methodology of Eye Movement-Contingent Display (EMCD) enables accurate control of the position and motion of the stimulus on the retina. EMCD procedures have been used successfully in many areas of vision science, including studies of visual attention, eye movements, and physiological characterization of neuronal response properties. Unfortunately, the difficulty of real-time programming and the unavailability of flexible and economical systems that can be easily adapted to the diversity of experimental needs and laboratory setups have prevented the widespread use of EMCD control. This paper describes EyeRIS, a general-purpose system for performing EMCD experiments on a Windows computer. Based on a digital signal processor with analog and digital interfaces, this integrated hardware and software system is responsible for sampling and processing oculomotor signals and subject responses and modifying the stimulus displayed on a CRT according to the gaze-contingent procedure specified by the experimenter. EyeRIS is designed to update the stimulus within a delay of 10 ms. To thoroughly evaluate EyeRIS' perforltlancc, this study (a) examines the response of the system in a number of EMCD procedures and computational benchmarking tests, (b) compares the accuracy of implementation of one particular EMCD procedure, retinal stabilization, to that produced by a standard tool used for this task, and (c) examines EyeRIS' performance in one of the many EMCD procedures that cannot be executed by means of any other currently available device.National Institute of Health (EY15732-01

Quark-antiquark interactions in background magnetic fields

Introduction - The properties of strong interacting matter in the presence of large external fields have attracted much interest in the recent past. The investigation of such properties is relevant in different physical conditions. For example, it is believed that strong magnetic fields, of the order of 1016 Tesla ∼ 1 GeV^2 , may have been produced in the early Universe. In addition, slightly lower magnetic fields, up to about 10^15 Tesla, are expected to be created in non-central ultra-relativistic heavy-ion collisions. In this context, the theory representing our current understanding of strong interaction, the Quantum Chromodynamics (QCD), allows to predict many important results. As regards the investigation in the non-perturbative regime, the lattice formulation (LQCD) reveals to be one of the most suitable approach. Within this framework, the properties of the strong interacting matter in the presence of external magnetic field have been studied extensively, leading to relevant results such as the effects on the QCD phase diagram at finite temperatures and those on of deconfinement and chiral system restauration. The work presented in this thesis lies exactly in this context. It is based on the study presented in a very recent paper 1 about the properties of the confining potential between two heavy quarks in the presence of a constant and uniform external magnetic field, performed within the LQCD formulation at zero temperature. It has been found that the potential is anisotropic for non-vanishing magnetic fields, showing different behaviours in the directions transverse and parallel to the external field. In particular, adopting the standard Cornell parametrization, i.e. a linear rising confining term (σr ) supplied with a Coulomb-like one (α/r ), it has been found that anisotropies emerge in both the string tension σ and in the strength of the Coulomb coupling α of the static potential, which acquire a non-trivial dependence on magnetic field, i.e. σ = σ(θ; B ) and α = α(θ; B ) with θ azimutal angle with respect to the direction of B . Controlling idea and methods - The original study proposed in this thesis is focused on the phenomelogical effects that such anisotropies may produce. The main idea is that the observed behaviour of the static quark-antiquark potential in the presence of strong magnetic fields should affect the observables directly related on it. To this aim, it has been chosen to follow two distinct lines of investigations. The first involves the direct effects of the anisotropic static quark-antiquark potential on the energy levels, i.e. the masses of the heavy-meson spectrum; the second, instead, generalizes the investigation at finite temperature and it focalized on the behaviour of the correlator between the so-called Polyakov loops L(x), defined as the temporal loop made up by the parallel transports (gauge links living) living on the lattice, which is strictly connected with the static potential. In the first case, the work has been based on an non-relativistic approach for describing the heavy-mesons, i.e. the bound states c c and b b. The reason lies exactly in the nature of the quenched potential, which is formally valid in the infinite mass limit and hence represents a suitable parametrization of the heavy quark-antiquark interaction. The model describing the dynamics of a bound state in an external magnetic field has been solved making use of a numerical algorithm (based on a finite-difference scheme) allowing the extraction of both eigenstates and eigenvalues through an Euclidean finite-time step evolution. This procedure, supplied with a state-mixing algorithm, has provided the computation of the masses of the lower part of the heavy-meson spectrum, i.e. that corresponding to the 1S and 1P states. Simulations have been performed in the range B = 0.1 − 0.3 GeV2 , both considering or not the presence of the anisotropy, in order to check and separate the possible mass differences. As regards the second part of this study, it is focused on the effects of external magnetic fields at finite temperature and, hence, representing a natural continuation of the investigation of the anisotropy. The expectation values of the Polyakov loop correlators have been extracted from lattice configuration samples corresponding to a 2+1 lattice QCD theory, i.e. with dynamical quarks u, d , s such that m_u = m_d =m_s . In order to check the possible effect of the magnetic anisotropy, correlators been computed separating the contributions along the spatial directions transverse and parallel with respect to the applied external magnetic field. Such a procedure also requires the application of a specific strategy to decrease the noise due to the UV fluctuation on the lattice (gauge link smearing). Simulations have been performed for different magnetic fields of the order of B ∼ 1015 Tesla and for a single lattice volume 32×8 at the temperature of about T ∼ 140 MeV, i.e. slightly before the expected chiral and deconfinement transitions. Obtained results - In both cases, the study suggests that the presence of an external strong magnetic field has relevant effects. Concerning the heavy-meson mass spectrum, the model predicts that the anisotropy, within the range investigated, may increase the mass value by an amount of the same order (or, in some cases, slightly higher) of those related to the effect of the magnetic field only. These are expected to be of the order of about 50-100 MeV in the case of the charmonium spectru, and of about 10 − 30 MeV for bottomonium states. In addition, the model predicts also non-trivial mixing between the particle states, depending on the module of the external field, which may creates concrete effects on, for example, the decay rates or the possible decay channels. Non-negligible effects have been also found, at finite temperature, on the correlator between Polyakov loops. Their behaviour for large distances seems to agree with the expected picture of a decreasing of the temperature of the confinement-deconfinement crossover in the presence of an external magnetic field. As regards the static quark-antiquark potential, a curve fitting procedure of the data suggest that for B = 0 there is a clear splitting between the shapes in the directions parallel and orthogonal with respect to the magnetc field axes. At the level of the string tension σ or the parameter α, the anisotropy effect is more noticeable and, as regards in particular the string tension, up to about 20 − 25% for |e|B ∼ 1 GeV2 . Such a study is clearly not exhaustive. Indeed, there are several lines of investigation which may be followed. As concerns the heavy-meson mass spectum, for example, one may try both to improve the non-relativistic model or to proceed with a more quantitative investigation about the reliability of a measurement of the observed effects. At finite temperatures, possible prospectives are more. Indeed, the study may be generalized to a wide range of both temperatures or densities, leading to a more detailed description of the possible effect on the QCD phase diagram