10,306 research outputs found
The exact radiation-reaction equation for a classical charged particle
An unsolved problem of classical mechanics and classical electrodynamics is
the search of the exact relativistic equations of motion for a classical
charged point-particle subject to the force produced by the action of its EM
self-field. The problem is related to the conjecture that for a classical
charged point-particle there should exist a relativistic equation of motion (RR
equation) which results both non-perturbative, in the sense that it does not
rely on a perturbative expansion on the electromagnetic field generated by the
charged particle and non-asymptotic, i.e., it does not depend on any
infinitesimal parameter. In this paper we intend to propose a novel solution to
this well known problem, and in particular to point out that the RR equation is
necessarily variational. The approach is based on two key elements: 1) the
adoption of the relativistic hybrid synchronous Hamilton variational principle
recently pointed out (Tessarotto et al, 2006). Its basic feature is that it can
be expressed in principle in terms of arbitrary "hybrid" variables (i.e.,
generally non-Lagrangian and non-Hamiltonian variables); 2) the variational
treatment of the EM self-field, taking into account the exact particle
dynamics.Comment: Contributed paper at RGD26 (Kyoto, Japan, July 2008
Hemisphere Mixing: a Fully Data-Driven Model of QCD Multijet Backgrounds for LHC Searches
A novel method is proposed here to precisely model the multi-dimensional
features of QCD multi-jet events in hadron collisions. The method relies on the
schematization of high-pT QCD processes as 2->2 reactions made complex by
sub-leading effects. The construction of libraries of hemispheres from
experimental data and the definition of a suitable nearest-neighbor-based
association map allow for the generation of artificial events that reproduce
with surprising accuracy the kinematics of the QCD component of original data,
while remaining insensitive to small signal contaminations. The method is
succinctly described and its performance is tested in the case of the search
for the hh->bbbb process at the LHC.Comment: 4 pages plus header, 1 figure, proceedings of EPS 2017 Venic
Vector bundles on the projective line and finite domination of chain complexes
Finitely dominated chain complexes over a Laurent polynomial ring in one
indeterminate are characterised by vanishing of their Novikov homology. We
present an algebro-geometric approach to this result, based on extension of
chain complexes to sheaves on the projective line. We also discuss the
K-theoretical obstruction to extension.Comment: v1: 11 page
Sensor networks security based on sensitive robots agents. A conceptual model
Multi-agent systems are currently applied to solve complex problems. The
security of networks is an eloquent example of a complex and difficult problem.
A new model-concept Hybrid Sensitive Robot Metaheuristic for Intrusion
Detection is introduced in the current paper. The proposed technique could be
used with machine learning based intrusion detection techniques. The new model
uses the reaction of virtual sensitive robots to different stigmergic variables
in order to keep the tracks of the intruders when securing a sensor network.Comment: 5 page
Neuronal assembly dynamics in supervised and unsupervised learning scenarios
The dynamic formation of groups of neurons—neuronal assemblies—is believed to mediate cognitive phenomena at many levels, but their detailed operation and mechanisms of interaction are still to be uncovered. One hypothesis suggests that synchronized oscillations underpin their formation and functioning, with a focus on the temporal structure of neuronal signals. In this context, we investigate neuronal assembly dynamics in two complementary scenarios: the first, a supervised spike pattern classification task, in which noisy variations of a collection of spikes have to be correctly labeled; the second, an unsupervised, minimally cognitive evolutionary robotics tasks, in which an evolved agent has to cope with multiple, possibly conflicting, objectives. In both cases, the more traditional dynamical analysis of the system’s variables is paired with information-theoretic techniques in order to get a broader picture of the ongoing interactions with and within the network. The neural network model is inspired by the Kuramoto model of coupled phase oscillators and allows one to fine-tune the network synchronization dynamics and assembly configuration. The experiments explore the computational power, redundancy, and generalization capability of neuronal circuits, demonstrating that performance depends nonlinearly on the number of assemblies and neurons in the network and showing that the framework can be exploited to generate minimally cognitive behaviors, with dynamic assembly formation accounting for varying degrees of stimuli modulation of the sensorimotor interactions
Resolved Kinematics of Runaway and Field OB Stars in the Small Magellanic Cloud
We use GAIA DR2 proper motions of the RIOTS4 field OB stars in the Small
Magellanic Cloud (SMC) to study the kinematics of runaway stars. The data
reveal that the SMC Wing has a systemic peculiar motion relative to the SMC Bar
of (v_RA, v_Dec) = (62 +/-7, -18+/-5) km/s and relative radial velocity +4.5
+/- 5.0 km/s. This unambiguously demonstrates that these two regions are
kinematically distinct: the Wing is moving away from the Bar, and towards the
Large Magellanic Cloud with a 3-D velocity of 64 +/- 10 km/s. This is
consistent with models for a recent, direct collision between the Clouds. We
present transverse velocity distributions for our field OB stars, confirming
that unbound runaways comprise on the order of half our sample, possibly more.
Using eclipsing binaries and double-lined spectroscopic binaries as tracers of
dynamically ejected runaways, and high-mass X-ray binaries (HMXBs) as tracers
of runaways accelerated by supernova kicks, we find significant contributions
from both populations. The data suggest that HMXBs have lower velocity
dispersion relative to dynamically ejected binaries, consistent with the former
corresponding to less energetic supernova kicks that failed to unbind the
components. Evidence suggests that our fast runaways are dominated by
dynamical, rather than supernova, ejections.Comment: Accepted to ApJ Letters. 10 pages, 4 figure
Contribution of water-limited ecoregions to their own supply of rainfall
The occurrence of wet and dry growing seasons in water-limited regions remains poorly understood, partly due to the complex role that these regions play in the genesis of their own rainfall. This limits the predictability of global carbon and water budgets, and hinders the regional management of naturalresources. Using novel satellite observations and atmospheric trajectory modelling, we unravel the origin and immediate drivers of growing-season precipitation, and the extent to which ecoregions themselves contribute to their own supply of rainfall. Results show that persistent anomalies in growing-season precipitation—and subsequent biomass anomalies—are caused by a complex interplay of land and ocean evaporation, air circulation and local atmospheric stability changes. For regions such as the Kalahari and Australia, the volumes of moisture recycling decline in dry years, providing a positive feedback that intensifies dry conditions. However, recycling ratios increase up to40%, pointing to the crucial role of these regions in generating their own supply of rainfall; transpiration in periods of water stress allows vegetation to partly offset the decrease in regional precipitation. Findings highlight the need to adequately represent vegetation–atmosphere feedbacks in models to predict biomass changes and to simulate the fate of water-limited regions in our warming climate
On the validity of the LAD and LL classical radiation-reaction equations
The search of the correct equation of motion for a classical charged particle
under the action of its electromagnetic (EM) self-field, the so-called
\textit{radiation-reaction equation of motion}, remains elusive to date. In
this paper we intend to point out why this is so. The discussion is based on
the direct construction of the EM self-potentials produced by a charged
spherical particle under the action of an external EM force. In particular we
intend to analyze basic features of the LAD (Lorentz-Abraham-Dirac) and the LL
(Landau-Lifschitz) equations. Both are shown to lead to incorrect or incomplete
results.Comment: Contributed paper at RGD26 (Kyoto,Japan, July 2008
Resonant Production of Scalar Diquarks at the Next Generation Electron-Positron Colliders
We investigate the potential of TESLA and JLC/NLC electron-positron linear
collider designs to observe diquarks produced resonantly in processes involving
hard photons.Comment: 14 pages, 8 figures, coded in RevTEX, uses epsfi
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