5,748 research outputs found
Plastic Representation of the Reachable Space for a Humanoid Robot
Reaching a target object requires accurate estimation of the object spatial position and its further transformation into a suitable arm-motor command. In this paper, we propose a framework that provides a robot with a capacity to represent its reachable space in an adaptive way. The location of the target is represented implicitly by both the gaze direction and the angles of arm joints. Two paired neural networks are used to compute the direct and inverse transformations between the arm position and the head position. These networks allow reaching the target either through a ballistic movement or through visually-guided actions. Thanks to the latter skill, the robot can adapt its sensorimotor transformations so as to reflect changes in its body configuration. The proposed framework was implemented on the NAO humanoid robot, and our experimental results provide evidences for its adaptative capabilities
Pre-hydrodynamic evolution in large and small systems
We extend our previous investigation of the effects of pre-hydrodynamic
evolution on final-state observables in heavy-ion collisions to smaller
systems. We use a state-of-the-art hybrid model for the numerical simulations
with optimal parameters obtained from a previous Bayesian study. By studying
p-Pb collisions, we find that the effects due to the assumption of a conformal
evolution in the pre-hydrodynamical stage are even more important in small
systems. We also show that this effect depends on the time duration of the
pre-equilibrium stage, which is further enhanced in small systems. Finally, we
show that the recent proposal of a free-streaming with subluminal velocity for
the pre-equilibrium stage, thus effectively breaking conformal invariance, can
alleviate the contamination of final state observables. Our study further
reinforces the need for moving beyond conformal approaches in pre-equilibrium
dynamics modeling, especially when extracting transport coefficients from
hybrid models in the high-precision era of heavy-ion collisions.Comment: 15 pages, 14 figure
Study of single muons with the Large Volume Detector at Gran Sasso Laboratory
The present study is based on the sample of about 3 mln single muons observed
by LVD at underground Gran Sasso Laboratory during 36500 live hours from June
1992 to February 1998. We have measured the muon intensity at slant depths from
3 km w.e. to 20 km w.e. Most events are high energy downward muons produced by
meson decay in the atmosphere. The analysis of these muons has revealed the
power index of pion and kaon spectrum: 2.76 \pm 0.05. The reminders are
horizontal muons produced by the neutrino interactions in the rock surrounding
LVD. The value of this flux is obtained. The results are compared with Monte
Carlo simulations and the world data.Comment: 13 pages, 2 figures, accepted for publication in "Physics of Atomic
Nuclei
The vitamin D grey areas in pediatric primary care. Very low serum 25-hydroxyvitamin D levels in asymptomatic children living in northeastern Italy
The principal questions about the vitamin D topic are far to be resolved: in which children 25-hydroxyvitamin D blood testing is appropriate and how much cholecalciferol should be given in the absence of the test? Analyzing vitamin D status in a group of children cared by a "family pediatrician" in northeastern Italy we noted a high incidence of deficiency in asymptomatic preschool children without risk factors. As routine vitamin D testing is not recommended in the average risk population the supplementation with cholecalciferol represents a "grey area" mostly in pediatric primary care
Muon `Depth -- Intensity' Relation Measured by LVD Underground Experiment and Cosmic-Ray Muon Spectrum at Sea Level
We present the analysis of the muon events with all muon multiplicities
collected during 21804 hours of operation of the first LVD tower. The measured
angular distribution of muon intensity has been converted to the `depth --
vertical intensity' relation in the depth range from 3 to 12 km w.e.. The
analysis of this relation allowed to derive the power index, , of the
primary all-nucleon spectrum: . The `depth -- vertical
intensity' relation has been converted to standard rock and the comparison with
the data of other experiments has been done. We present also the derived
vertical muon spectrum at sea level.Comment: 7 pages, 3 figures, to be published on Phys. Rev.
Upper Limit on the Prompt Muon Flux Derived from the LVD Underground Experiment
We present the analysis of the muon events with all muon multiplicities
collected during 21804 hours of operation of the first LVD tower. The measured
depth-angular distribution of muon intensities has been used to obtain the
normalization factor, A, the power index, gamma, of the primary all-nucleon
spectrum and the ratio, R_c, of prompt muon flux to that of pi-mesons - the
main parameters which determine the spectrum of cosmic ray muons at the sea
level. The value of gamma = 2.77 +/- 0.05 (68% C.L.) and R_c < 2.0 x 10^-3 (95%
C.L.) have been obtained. The upper limit to the prompt muon flux favours the
models of charm production based on QGSM and the dual parton model.Comment: 10 pages, 4 figures, RevTex. To appear in Phys. Rev.
Neutron Majorana mass from exotic instantons
We show how a Majorana mass for the Neutron could result from
non-perturbative quantum gravity effects peculiar to string theory. In
particular, "exotic instantons" in un-oriented string compactifications with
D-branes extending the (supersymmetric) standard model could indirectly produce
an effective operator delta{m} n^t n+h.c. In a specific model with an extra
vector-like pair of `quarks', acquiring a large mass proportional to the string
mass scale (exponentially suppressed by a function of the string moduli
fields), delta{m} can turn out to be as low as 10^{-24}-10^{-25} eV. The
induced neutron-antineutron oscillations could take place with a time scale
tau_{n\bar{n}} > 10^8 s, that could be tested by the next generation of
experiments. On the other hand, proton decay and FCNC's are automatically
strongly suppressed and are compatible with the current experimental limits.
Depending on the number of brane intersections, the model may also lead to the
generation of Majorana masses for R-handed neutrini. Our proposal could also
suggest neutron-neutralino or neutron-axino oscillations, with implications in
UCN, Dark Matter Direct Detection, UHECR and Neutron-Antineutron oscillations.
This suggests to improve the limits on neutron-antineutron oscillations, as a
possible test of string theory and quantum gravity.Comment: 35 pages, 11 figures. More comments on neutron-neutralino mixin
Highlights from the Pierre Auger Observatory
The Pierre Auger Observatory is the world's largest cosmic ray observatory.
Our current exposure reaches nearly 40,000 km str and provides us with an
unprecedented quality data set. The performance and stability of the detectors
and their enhancements are described. Data analyses have led to a number of
major breakthroughs. Among these we discuss the energy spectrum and the
searches for large-scale anisotropies. We present analyses of our X
data and show how it can be interpreted in terms of mass composition. We also
describe some new analyses that extract mass sensitive parameters from the 100%
duty cycle SD data. A coherent interpretation of all these recent results opens
new directions. The consequences regarding the cosmic ray composition and the
properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray
Conference, Rio de Janeiro 201
Measurement of the t(t)over-bar production cross section in the dilepton channel in pp collisions at √s=8 TeV
The top-antitop quark (t (t) over bar) production cross section is measured in proton-proton collisions at root s = 8 TeV with the CMS experiment at the LHC, using a data sample corresponding to an integrated luminosity of 5.3 fb(-1). The measurement is performed by analysing events with a pair of electrons or muons, or one electron and one muon, and at least two jets, one of which is identified as originating from hadronisation of a bottom quark. The measured cross section is 239 +/- 2 (stat.) +/- 11 (syst.) +/- 6 (lum.) pb, for an assumed top-quark mass of 172.5 GeV, in agreement with the prediction of the standard model
The Pierre Auger Observatory III: Other Astrophysical Observations
Astrophysical observations of ultra-high-energy cosmic rays with the Pierre
Auger ObservatoryComment: Contributions to the 32nd International Cosmic Ray Conference,
Beijing, China, August 201
- …