206 research outputs found
High-level environment representations for mobile robots
In most robotic applications we are faced with the problem of building
a digital representation of the environment that allows the robot to
autonomously complete its tasks. This internal representation can be
used by the robot to plan a motion trajectory for its mobile base
and/or end-effector. For most man-made environments we do not have
a digital representation or it is inaccurate. Thus, the robot must
have the capability of building it autonomously. This is done by
integrating into an internal data structure incoming sensor
measurements. For this purpose, a common solution consists in solving
the Simultaneous Localization and Mapping (SLAM) problem. The map
obtained by solving a SLAM problem is called ``metric'' and it
describes the geometric structure of the environment. A metric map is
typically made up of low-level primitives (like points or
voxels). This means that even though it represents the shape of the
objects in the robot workspace it lacks the information of which
object a surface belongs to. Having an object-level representation of
the environment has the advantage of augmenting the set of possible
tasks that a robot may accomplish. To this end, in this thesis we
focus on two aspects. We propose a formalism to represent in a uniform
manner 3D scenes consisting of different geometric primitives,
including points, lines and planes. Consequently, we derive a local
registration and a global optimization algorithm that can exploit this
representation for robust estimation. Furthermore, we present a
Semantic Mapping system capable of building an \textit{object-based}
map that can be used for complex task planning and execution. Our
system exploits effective reconstruction and recognition techniques
that require no a-priori information about the environment and can be
used under general conditions
flavour symmetries as Peccei-Quinn symmetries
We investigate to what extent a generic, generation-dependent symmetry
acting on the quark Yukawa operators can reduce the number of free parameters
by forcing some entries in the Yukawa matrices to vanish. The maximal reduction
compatible with CP violation yields nine real parameters and one phase, which
matches the number of physical observables, implying that such models have no
free parameters. We derive a set of results: (i) the only possible structures
have the form , where the subscripts indicate the number of
real parameters in the Yukawa matrices, (ii) there are only two inequivalent
Yukawa structures, each one giving rise to six different models depending on
quark flavour assignments, (iii) the symmetries that generate these
textures all have a QCD anomaly, and hence are Peccei-Quinn symmetries,
reinforcing the idea of a possible connection between the quark flavour puzzle
and the axion solution to the strong CP problem, (iv) in some cases the
contributions to the QCD anomaly of two generations cancels out, and this opens
the possibility that the axion coupling to nucleons could be strongly
suppressed. Flavour-violating axion couplings to quarks are completely fixed,
up to the axion decay constant, providing a non-trivial complementarity between
low-energy flavour-violating processes and standard axion searches.Comment: v2: version accepted for publication in JHEP; figure 1 updated; minor
additions; 23 pages, 1 figure. v1: 20 pages, 1 figur
Rigid tool affordance matching points of regard
In this abstract we briefly introduce the analysis of simple rigid object affordance by experimentally establishing the relation between the point of regard of subjects before grasping an object and the finger tip points of contact once the object is grasped. The analysis show that there is a strong relation between these data, in so justifying the hypothesis that people figures out how objects are afforded according to their functionality
Window for preferred axion models
We discuss phenomenological criteria for defining “axion windows,” namely regions in the parameter space of the axion-photon coupling where realistic models live. Currently, the boundaries of this region depend on somewhat arbitrary criteria, and it would be highly desirable to specify them in terms of precise phenomenological requirements. We first focus on hadronic axion models within post-inflationary scenarios, in which the initial abundance of the new vectorlike quarks Q is thermal. We classify their representations R Q by requiring that (i) the Q are sufficiently short lived to avoid issues with long-lived strongly interacting relics, (ii) the theory remains weakly coupled up to the Planck scale. The more general case of multiple R Q is also studied, and the absolute upper and lower bounds on the axion-photon coupling as a function of the axion mass is identified. Pre-inflationary scenarios in which the axion decay constant remains bounded as f a ≤ 5 × 10 11 GeV allow for axion-photon couplings only about 20% larger. Realistic Dine-Fischler-Srednicki-Zhitnitsky type of axion models also remain encompassed within the hadronic axion window. Some mechanisms that can allow to enhance the axion-photon coupling to values sizeably above the preferred window are discussed
Component-wise modeling of articulated objects
We introduce a novel framework for modeling articulated objects based on the aspects of their components. By decomposing the object into components, we divide the problem in smaller modeling tasks. After obtaining 3D models for each component aspect by employing a shape deformation paradigm, we merge them together, forming the object components. The final model is obtained by assembling the components using an optimization scheme which fits the respective 3D models to the corresponding apparent contours in a reference pose. The results suggest that our approach can produce realistic 3D models of articulated objects in reasonable time
Covert symmetries in the neutrino mass matrix
The flavour neutrino puzzle is often addressed by considering neutrino mass matrices m with a certain number of vanishing entries (mij = 0 for some values of the indices), since a reduction in the number of free parameters increases the predictive power. Symmetries that can enforce textures zero can also enforce a more general type of conditions f(mij) = 0 with f some function of the matrix elements mij. In this case m can have all entries non-vanishing with no reduction in its predictive power. We classify all generation-dependent U(1) symmetries which, in the presence of two leptonic Higgs doublets, can reduce the number of independent high-energy parameters of type-I seesaw to the minimum number compatible with non-vanishing neutrino mixings and CP violation. These symmetries are broken above the scale where the effective operator is generated and can thus remain covert, in the sense that no explicit evidence of the symmetry can be read off the neutrino mass matrix, and different symmetries can give rise to the same low-energy structure. We find that only two cases are viable: one yields a structure with two zero-textures already considered in the literature, the other has no zero-textures and has never been considered before. It predicts normal ordering, a lightest neutrino mass ∼ 10 meV, a Dirac phase δ ∼ 3π2 and definite values for the Majorana phases
Loss of phosphoserine polar group asymmetry and inhibition of cholesterol transport in Jurkat cells treated with cholesterylphosphoserine
Abstract Cholesterylphosphoserine (CPHS) is a synthetic ester of cholesterol showing immunosuppressive activity. In the present study, we have used the T cell line Jurkat to investigate its mechanism of action. CPHS incorporates into cells reaching a molar ratio of 0.23 and 3.9 with the total phospholipid and cholesterol content, without inducing necrosis or apoptosis. CPHS incorporation elicits a dose-dependent binding of fluorescein isothiocyanate-labeled annexin V, suggesting that the steroid distributes in the external leaflet of plasma membrane exposing the phosphoserine group to the external cell environment and inserting the steroid ring into the phospholipid bilayer. In agreement with a preferential steroid association with sphingolipids, CPHS is included in a Triton X-100-insoluble complex when mixed with sphingomyelin and cholesterol. CPHS incorporation inhibits the esterification of low density lipoprotein (LDL)-derived cholesterol, producing a minor influence on the endogenous synthesis of cholesterol and on the acyl-CoA:cholesterol acyltransferase activity. In this effect, CPHS is as potent as progesterone (IC50 of 3.5 μ m ). It is concluded that the insertion of cholesterylphosphoserine (CPHS) in the Jurkat plasma membrane neutralizes the asymmetric distribution of the phosphoserine group and inhibits the movement of cholesterol to the endoplasmic reticulum. As CPHS is a negatively charged steroid, this last effect may be linked to the perturbation of sphingolipid/cholesterol-based microdomains, proposed to play a role in cholesterol trafficking.—Cusinato, F., W. Habeler, F. Calderazzo, F. Nardi, and A. Bruni. Loss of phosphoserine polar group asymmetry and inhibition of cholesterol transport in Jurkat cells treated with cholesterylphosphoserine
Solar axions cannot explain the XENON1T excess
We argue that the interpretation in terms of solar axions of the recent
XENON1T excess is not tenable when confronted with astrophysical observations
of stellar evolution. We discuss the reasons why the emission of a flux of
solar axions sufficiently intense to explain the anomalous data would radically
alter the distribution of certain type of stars in the color-magnitude diagram
in first place, and would also clash with a certain number of other
astrophysical observables. Quantitatively, the significance of the discrepancy
ranges from for the rate of period change of pulsating White
Dwarfs, and exceedes for the -parameter and for .Comment: 6 pages, 2 figures, 1 table. Version accepted for publication on PR
Axion-electron decoupling in nucleophobic axion models
The strongest upper bounds on the axion mass come from astrophysical observations like the neutrino burst duration of SN1987A, which depends on the axion couplings to nucleons, or the white-dwarf cooling rates and red-giant evolution, which involve the axion-electron coupling. It has been recently argued that in variants of Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) models with generation-dependent Peccei-Quinn charges an approximate axion-nucleon decoupling can occur, strongly relaxing the SN1987A bound. However, as in standard DFSZ models, the axion remains in general coupled to electrons, unless an ad hoc cancellation is engineered. Here we show that axion-electron decoupling can be implemented without extra tunings in DFSZ-like models with three Higgs doublets. Remarkably, the numerical value of the quark mass ratio m u / m d ∼ 1 / 2 is crucial to open up this possibility
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