8,263 research outputs found
How Mayors Perceive the Influence of Social Media on the Policy Cycle
Information technology clearly influences the decision-making behaviour of individuals, groups, and organisations. In particular, social media and Web 2.0 technologies can affect the rationality and effectiveness of the policy cycle in the public sector. This growing influence deserves to be analysed. This work aims to understand how the influence of social media in the different phases of the policy cycle is perceived by mayors, the main decision-makers in local governments
On Embeddability of Buses in Point Sets
Set membership of points in the plane can be visualized by connecting
corresponding points via graphical features, like paths, trees, polygons,
ellipses. In this paper we study the \emph{bus embeddability problem} (BEP):
given a set of colored points we ask whether there exists a planar realization
with one horizontal straight-line segment per color, called bus, such that all
points with the same color are connected with vertical line segments to their
bus. We present an ILP and an FPT algorithm for the general problem. For
restricted versions of this problem, such as when the relative order of buses
is predefined, or when a bus must be placed above all its points, we provide
efficient algorithms. We show that another restricted version of the problem
can be solved using 2-stack pushall sorting. On the negative side we prove the
NP-completeness of a special case of BEP.Comment: 19 pages, 9 figures, conference version at GD 201
The Low Frequency Instrument in the ESA Planck mission
Measurements of the cosmic microwave background (CMB) allow high precision
observation of the cosmic plasma at redshift z~1100. After the success of the
NASA satellite COBE, that in 1992 provided the first detection of the CMB
anisotropy, results from many ground-based and balloon-borne experiments have
showed a remarkable consistency between different results and provided
quantitative estimates of fundamental cosmological properties. During the
current year the team of the NASA WMAP satellite has released the first
improved full-sky maps of the CMB since COBE, leading to a deeper insight in
the origin and evolution of the Universe. The ESA satellite Planck, scheduled
for launch in 2007, is designed to provide the ultimate measurement of the CMB
temperature anisotropy over the full sky, with an accuracy that will be limited
only by astrophysical foregrounds, and robust detection of polarisation
anisotropy. Planck will observe the sky with two instruments over a wide
spectral band (the Low Frequency Instrument, based on coherent radiometers,
from 30 to 70 GHz and the High Frequency Instrument, based on bolometric
detectors, from 100 to 857 GHz). The mission performances will improve
dramatically the scientific return compared to WMAP. Furthermore the LFI
radiometers (as well as some of the HFI bolometers) are intrinsically sensitive
to polarisation so that by combining the data from different receivers it will
be possible to measure accurately the E mode and to detect the B mode of the
polarisation power spectrum. Planck sensitivity will offer also the possibility
to detect the non-Gaussianities imprinted in the CMB.Comment: 4 pages, 2 figures, to appear in "Proc of International Symposium on
Plasmas in the Laboratory and in the Universe: new insights and new
challenges", September 16-19, 2003, Como, Ital
Modélisation 3D des façades de bâtiments des anciennes Médina
Le LIDAR (Light Detecting and Ranging) terrestre statique est un outil de levé présentant actuellement une source de données 3D indispensable dans l’évaluation et la surveillance des bâtiments patrimoniaux. A travers des processus automatiques de modélisation 3D, la manipulation de cette source de données dans des outils de communication devient plus souple. Le processus de modélisation 3D impose des sous missions indispensables dont la segmentation. Une grande partie des approches de segmentation se focalisent sur l’emploi des composantes géométriques en exploitant la représentation mathématique d’une surface plane ou courbée. En raison de la complexité de l’architecture des façades, une segmentation utilisant uniquement l’aspect géométrique reste insuffisante. Ainsi, une nouvelle approche de segmentation est développée équilibrant les résultats de l’extraction des surfaces homogènes. Ceci, en se basant sur l’ensemble des composantes d’un nuage de points coloriés à savoir les composantes géométriques, les valeurs RGB et les intensités laser des détails constituant les façades des bâtiments des anciennes Médina. Le processus s’initialise par l’extraction des segments plans à l’aide de l’algorithme RANSAC. Le résultat fera l’objet d’une deuxième segmentation radiométrique basée sur l’introduction du critère de similarité couleur dans l’algorithme de croissance de région. Enfin une fusion de classes sera effectuée en fonction de la similarité de l’intensité laser.
The static terrestrial LIDAR is a tool of surveying which present a vital source of 3D data in the heritage buildings evaluation and monitoring. Through automated 3D modeling process, manipulating this data source in communication tools becomes more flexible. The 3D modeling process imposes on essential tasks including segmentation. Much of segmentation approaches focus on the use of geometric components by exploiting the mathematical representation of a plane or curved area. Due to the complexity of the facades architecture, segmentation using only the geometrical aspect is insufficient. Thus, a new segmentation approach is developed balancing the results of extracting homogeneous areas based on all colored point cloud components namely geometric data, the RGB values and intensities of facades details especially in old Medina building. The process consists of the planar segments extracting using the RANSAC algorithm. The result will be subject to radiometric segmentation through the introduction of color similarity criterion in the region growing algorithm and finally a fusion of classes based on the intensity’s similarity
Planck pre-launch status: calibration of the Low Frequency Instrument flight model radiometers
The Low Frequency Instrument (LFI) on-board the ESA Planck satellite carries
eleven radiometer subsystems, called Radiometer Chain Assemblies (RCAs), each
composed of a pair of pseudo-correlation receivers. We describe the on-ground
calibration campaign performed to qualify the flight model RCAs and to measure
their pre-launch performances. Each RCA was calibrated in a dedicated
flight-like cryogenic environment with the radiometer front-end cooled to 20K
and the back-end at 300K, and with an external input load cooled to 4K. A
matched load simulating a blackbody at different temperatures was placed in
front of the sky horn to derive basic radiometer properties such as noise
temperature, gain, and noise performance, e.g. 1/f noise. The spectral response
of each detector was measured as was their susceptibility to thermal variation.
All eleven LFI RCAs were calibrated. Instrumental parameters measured in these
tests, such as noise temperature, bandwidth, radiometer isolation, and
linearity, provide essential inputs to the Planck-LFI data analysis.Comment: 15 pages, 18 figures. Accepted for publication in Astronomy and
Astrophysic
Reconstructing Seesaws
We explore some aspects of "reconstructing" the heavy singlet sector of
supersymmetric type I seesaw models, for two, three or four singlets. We work
in the limit where one light neutrino is massless. In an ideal world, where
selected coefficients of the TeV-scale effective Lagrangian could be measured
with arbitrary accuracy, the two-singlet case can be reconstructed, two three
or more singlets can be differentiated, and an inverse seesaw with four
singlets can be reconstructed. In a more realistic world, we estimate \ell_\a
\to \ell_\b \gamma expectations with a "Minimal-Flavour-Violation-like"
ansatz, which gives a relation between ratios of the three branching ratios.
The two singlet model predicts a discrete set of ratios.Comment: 14 page
Measurement of Branching Fractions and Rate Asymmetries in the Rare Decays B -> K(*) l+ l-
In a sample of 471 million BB events collected with the BABAR detector at the
PEP-II e+e- collider we study the rare decays B -> K(*) l+ l-, where l+ l- is
either e+e- or mu+mu-. We report results on partial branching fractions and
isospin asymmetries in seven bins of di-lepton mass-squared. We further present
CP and lepton-flavor asymmetries for di-lepton masses below and above the J/psi
resonance. We find no evidence for CP or lepton-flavor violation. The partial
branching fractions and isospin asymmetries are consistent with the Standard
Model predictions and with results from other experiments.Comment: 16 pages, 14 figures, accepted by Phys. Rev.
Improved Limits on decays to invisible final states
We establish improved upper limits on branching fractions for B0 decays to
final States 10 where the decay products are purely invisible (i.e., no
observable final state particles) and for final states where the only visible
product is a photon. Within the Standard Model, these decays have branching
fractions that are below the current experimental sensitivity, but various
models of physics beyond the Standard Model predict significant contributions
for these channels. Using 471 million BB pairs collected at the Y(4S) resonance
by the BABAR experiment at the PEP-II e+e- storage ring at the SLAC National
Accelerator Laboratory, we establish upper limits at the 90% confidence level
of 2.4x10^-5 for the branching fraction of B0-->Invisible and 1.7x10^-5 for the
branching fraction of B0-->Invisible+gammaComment: 8 pages, 3 postscript figures, submitted to Phys. Rev. D (Rapid
Communications
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Measurement of B(B-->X_s {\gamma}), the B-->X_s {\gamma} photon energy spectrum, and the direct CP asymmetry in B-->X_{s+d} {\gamma} decays
The photon spectrum in B --> X_s {\gamma} decay, where X_s is any strange
hadronic state, is studied using a data sample of (382.8\pm 4.2) \times 10^6
e^+ e^- --> \Upsilon(4S) --> BBbar events collected by the BABAR experiment at
the PEP-II collider. The spectrum is used to measure the branching fraction B(B
--> X_s \gamma) = (3.21 \pm 0.15 \pm 0.29 \pm 0.08)\times 10^{-4} and the
first, second, and third moments = 2.267 \pm 0.019 \pm 0.032 \pm
0.003 GeV,, )^2> = 0.0484 \pm 0.0053 \pm 0.0077 \pm
0.0005 GeV^2, and )^3> = -0.0048 \pm 0.0011 \pm 0.0011
\pm 0.0004 GeV^3, for the range E_\gamma > 1.8 GeV, where E_{\gamma} is the
photon energy in the B-meson rest frame. Results are also presented for
narrower E_{\gamma} ranges. In addition, the direct CP asymmetry A_{CP}(B -->
X_{s+d} \gamma) is measured to be 0.057 \pm 0.063. The spectrum itself is also
unfolded to the B-meson rest frame; that is the frame in which theoretical
predictions for its shape are made.Comment: 37 pages, 19 postscript figures, submitted to Phys. Rev. D. No
analysis or results have changed from previous version. Some changes to
improve clarity based on interactions with Phys. Rev. D referees, including
one new Figure (Fig. 13), and some minor wording/punctuation/spelling
mistakes fixe
Search for lepton-number violating processes in B+ -> h- l+ l+ decays
We have searched for the lepton-number violating processes B+ -> h- l+ l+
with h- = K-/pi- and l+ = e+/mu+, using a sample of 471+/-3 million BBbar
events collected with the BaBar detector at the PEP-II e+e- collider at the
SLAC National Accelerator Laboratory. We find no evidence for these decays and
place 90% confidence level upper limits on their branching fractions Br(B+ ->
pi- e+ e+) K- e+ e+) pi-
mu+ mu+) K- mu+ mu+) < 6.7 x 10^{-8}.Comment: 8 pages, 4 postscript figures, submitted to Phys. Rev. D. R
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