3,797 research outputs found
A step backward for Italy\u27s meritocracy.
Italian scientists have long lamented the lack of resources, political attention, and meritocracy in assigning taxpayers’ money
Casimir-Polder forces between two accelerating atoms and the Unruh effect
The Casimir-Polder force between two atoms with equal uniform acceleration
and separated by a constant distance R is considered. We show that, in the
low-acceleration limit, while the near-zone R^{-6} behavior of the interatomic
interaction energy is not changed by the acceleration of the atoms, the
far-zone interaction energy decreases as R^{-5} instead of the well-known
R^{-7} behavior for inertial atoms. Possibility of an indirect detection of the
Unruh effect through measurements of the Casimir-Polder force between the two
accelerating atoms is also suggested. We also consider a heuristic model for
calculating the Casimir-Polder potential energy between the two atoms in the
high-acceleration limit.Comment: Contribution to the Proceedings of the QFEXT09 Conference, Norman,
Oklahoma, US
Trajectory optimization and motion planning for quadrotors in unstructured environments
Trajectory optimization and motion planning for quadrotors in
unstructured environments
Coming out from university labs robots perform tasks usually navigating through
unstructured environment. The realization of autonomous motion in such type of environments
poses a number of challenges compared to highly controlled laboratory
spaces. In unstructured environments robots cannot rely on complete knowledge
of their sorroundings and they have to continously acquire information for decision
making. The challenges presented are a consequence of the high-dimensionality
of the state-space and of the uncertainty introduced by modeling and perception.
This is even more true for aerial-robots that has a complex nonlinear dynamics a can
move freely in 3D-space. To avoid this complexity a robot have to select a small set of
relevant features, reason on a reduced state space and plan trajectories on short-time
horizon. This thesis is a contribution towards the autonomous navigation of aerial
robots (quadrotors) in real-world unstructured scenarios. The first three chapters
present a contribution towards an implementation of Receding Time Horizon Optimal
Control. The optimization problem for a model based trajectory generation in
environments with obstacles is set, using an approach based on variational calculus
and modeling the robots in the SE(3) Lie Group of 3D space transformations. The
fourth chapter explores the problem of using minimal information and sensing to
generate motion towards a goal in an indoor bulding-like scenario. The fifth chapter
investigate the problem of extracting visual features from the environment to
control the motion in an indoor corridor-like scenario. The last chapter deals with
the problem of spatial reasoning and motion planning using atomic proposition in a
multi-robot environments with obstacles
Galaxy evolution in nearby galaxy groups. III. A GALEX view of NGC 5846, the largest group in the local universe
We explore the co-evolution of galaxies in nearby groups (V < 3000 km/s) with
a multi-wavelength approach. We analyze GALEX far-UV (FUV) and near-UV (NUV)
imaging and SDSS u,g,r,i,z data of groups spanning a large range of dynamical
phases. We characterize the photometric properties of
spectroscopically-confirmed galaxy members and investigate the global
properties of the groups through a dynamical analysis. Here we focus on NGC
5846, the third most massive association of Early-Type Galaxies (ETG) after the
Virgo and Fornax clusters. The group, composed of 90 members, is dominated by
ETGs (about 80 per cent), and among ETGs about 40\% are dwarfs. Results are
compared with those obtained for three groups in the LeoII cloud, which are
radically different both in member-galaxy population and dynamical properties.
The FUV-NUV cumulative colour distribution and the normalized UV luminosity
function (LF) significantly differ due to the different fraction of late-type
galaxy population. The UV LF of NGC 5846 resembles that of the Virgo cluster,
however our analysis suggests that star-formation episodes are still occurring
in most of the group galaxies, including ETGs. The NUV-i colour distribution,
the optical-UV colour-colour diagram, and NUV-r vs. Mr colour-magnitude
relation suggest that the gas contribution cannot be neglected in the evolution
of ETG-type group members. Our analysis highlights that NGC~5846 is still in an
active phase of its evolution, notwithstanding the dominance of dwarf and
bright ETGs and its virialized configuration.Comment: 26 pages, 13 figures, accepted for publication in MNRA
Effects of a uniform acceleration on atom-field interactions
We review some quantum electrodynamical effects related to the uniform
acceleration of atoms in vacuum. After discussing the energy level shifts of a
uniformly accelerated atom in vacuum, we investigate the atom-wall
Casimir-Polder force for accelerated atoms, and the van der
Waals/Casimir-Polder interaction between two accelerated atoms. The possibility
of detecting the Unruh effect through these phenomena is also discussed in
detail.Comment: 6 pages. Special Issue: 20th Central European Workshop on Quantum
Optics - Stockholm - June 201
Prototipo di bollettino mensile di bilancio idrologico in atmosfera nella regione mediterranea: simulazione numerica con un modello meteorologico nei due trimestri prototipali
La presente relazione riassume l'attività svolta nell'ambito della prima fase della convenzione CRS4-DSTNPC \prototipo del bollettino mensile di bilancio idrologico in atmosfera". In particolare è descritta l'analisi delle metodologie utilizzabili rispetto agli obbiettivi del progetto, i criteri addottati per la selezione dei due periodi prototipali e le integrazioni numeriche ottenute mediante il Modello di circolazione atmosferica ad Area Limitata (LAM) nei due periodi trimestrali scelti. Vengono discussi, inoltre, il bilancio idrologico atmosferico ottenuto utilizzando le analisi meteorologiche e le medie mensili di precipitazione sulla Sardegna relativamente al periodo dal 1986 al 1988 e presentata una descrizione del
codice LAM (BOLAM) utilizzato per eseguire i run previsti dalla convenzione
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