20,353 research outputs found
A new formulation of compartmental epidemic modelling for arbitrary distributions of incubation and removal times
The paradigm for compartment models in epidemiology assumes exponentially
distributed incubation and removal times, which is not realistic in actual
populations. Commonly used variations with multiple exponentially distributed
variables are more flexible, yet do not allow for arbitrary distributions. We
present a new formulation, focussing on the SEIR concept that allows to include
general distributions of incubation and removal times. We compare the solution
to two types of agent-based model simulations, a spatially homogeneous one
where infection occurs by proximity, and a model on a scale-free network with
varying clustering properties, where the infection between any two agents
occurs via their link if it exists. We find good agreement in both cases.
Furthermore a family of asymptotic solutions of the equations is found in terms
of a logistic curve, which after a non-universal time shift, fits extremely
well all the microdynamical simulations. The formulation allows for a simple
numerical approach; software in Julia and Python is provided.Comment: 21 pages, 11 figures. v2 matches published version: improved
presentation (including title, abstract and references), results and
conclusions unchange
Majorana vs Pseudo-Dirac Neutrinos at the ILC
Neutrino masses could originate in seesaw models testable at colliders, with
light mediators and an approximate lepton number symmetry. The minimal model of
this type contains two quasi-degenerate Majorana fermions forming a
pseudo-Dirac pair. An important question is to what extent future colliders
will have sensitivity to the splitting between the Majorana components, since
this quantity signals the breaking of lepton number and is connected to the
light neutrino masses. We consider the production of these neutral heavy
leptons at the ILC, where their displaced decays provide a golden signal: a
forward-backward charge asymmetry, which depends crucially on the mass
splitting between the two Majorana components. We show that this observable can
constrain the mass splitting to values much lower than current bounds from
neutrinoless double beta decay and natural loop corrections.Comment: 16 pages, 5 figures; v2: Minor changes, version accepted for
publication in EPJ
Standard Model Baryogenesis
Simply on CP arguments, we argue against a Standard Model explanation of
baryogenesis via the charge transport mechanism. A CP-asymmetry is found in the
reflection coefficients of quarks hitting the electroweak phase boundary
created during a first order phase transition. The problem is analyzed both in
an academic zero temperature case and in the realistic finite temperature one.
At finite temperature, a crucial role is played by the damping rate of
quasi-quarks in a hot plasma, which induces loss of spatial coherence and
suppresses reflection on the boundary even at tree-level. The resulting baryon
asymmetry is many orders of magnitude below what observation requires. We
comment as well on related works.Comment: 10 pages, CERN-TH. 7368/94, LPTHE Orsay-94/71, HD-THEP-94-2
Correlation functions at small quark masses with overlap fermions
We report on recent work on the determination of low-energy constants
describing Delta{S}=1 weak transitions, in order to investigate the origins of
the Delta{I}=1/2 rule. We focus on numerical techniques designed to enhance the
statistical signal in three-point correlation functions computed with overlap
fermions near the chiral limit.Comment: Talk presented at Lattice2004(weak), Fermilab, 21-26 June 2004, 3
pages, 2 figure
Flexible Authentication in Vehicular Ad hoc Networks
A Vehicular Ad-Hoc Network (VANET) is a form of Mobile ad-hoc network, to
provide communications among nearby vehicles and between vehicles and nearby
fixed roadside equipment. The key operation in VANETs is the broadcast of
messages. Consequently, the vehicles need to make sure that the information has
been sent by an authentic node in the network. VANETs present unique challenges
such as high node mobility, real-time constraints, scalability, gradual
deployment and privacy. No existent technique addresses all these requirements.
In particular, both inter-vehicle and vehicle-to-roadside wireless
communications present different characteristics that should be taken into
account when defining node authentication services. That is exactly what is
done in this paper, where the features of inter-vehicle and vehicle-to-roadside
communications are analyzed to propose differentiated services for node
authentication, according to privacy and efficiency needs
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