26 research outputs found
Mean-field limit and Semiclassical Expansion of a Quantum Particle System
We consider a quantum system constituted by identical particles
interacting by means of a mean-field Hamiltonian. It is well known that, in the
limit , the one-particle state obeys to the Hartree equation.
Moreover, propagation of chaos holds. In this paper, we take care of the
dependence by considering the semiclassical expansion of the
-particle system. We prove that each term of the expansion agrees, in the
limit , with the corresponding one associated with the Hartree
equation. We work in the classical phase space by using the Wigner formalism,
which seems to be the most appropriate for the present problem.Comment: 44 pages, no figure
A Kac model for kinetic annihilation
In this paper we consider the stochastic dynamics of a finite system of
particles in a finite volume (Kac-like particle system) which annihilate with
probability or collide elastically with probability
. We first establish the well-posedness of the particle system which
exhibits no conserved quantities. We rigorously prove that, in some
thermodynamic limit, a suitable hierarchy of kinetic equations is recovered for
which tensorized solution to the homogenous Boltzmann with annihilation is a
solution. For bounded collision kernels, this shows in particular that
propagation of chaos holds true. Furthermore, we make conjectures about the
limit behaviour of the particle system when hard-sphere interactions are taken
into account.Comment: 40 page
Derivation of the Fick's Law for the Lorentz Model in a low density regime
We consider the Lorentz model in a slab with two mass reservoirs at the
boundaries. We show that, in a low density regime, there exists a unique
stationary solution for the microscopic dynamics which converges to the
stationary solution of the heat equation, namely to the linear profile of the
density. In the same regime the macroscopic current in the stationary state is
given by the Fick's law, with the diffusion coefficient determined by the
Green-Kubo formula.Comment: 33 pages, 7 figure
Analytical approach to relaxation dynamics of condensed Bose gases
The temporal evolution of a perturbation of the equilibrium distribution of a
condensed Bose gas is investigated using the kinetic equation which describes
collision between condensate and noncondensate atoms. The dynamics is studied
in the low momentum limit where an analytical treatment is feasible. Explicit
results are given for the behavior at large times in different temperature
regimes.Comment: 25 pages, 3 figures. Typos corrected. Final version to appear in
Annals of Physic
Semiclassical Propagation of Coherent States for the Hartree equation
In this paper we consider the nonlinear Hartree equation in presence of a
given external potential, for an initial coherent state. Under suitable
smoothness assumptions, we approximate the solution in terms of a time
dependent coherent state, whose phase and amplitude can be determined by a
classical flow. The error can be estimated in by C \sqrt {\var}, \var
being the Planck constant. Finally we present a full formal asymptotic
expansion
Diagnosis of Imported Dengue and Zika Virus Infections in Italy from November 2015 to November 2022: Laboratory Surveillance Data from a National Reference Laboratory
Dengue (DENV) and Zika (ZIKV) viruses are mosquito-borne human pathogens. In Italy,
the presence of the competent vector Aedes albopictus increases the risk of autochthonous transmission,
and a national plan for arboviruses prevention, surveillance, and response (PNA 2020–2025) is in
place. The results of laboratory diagnosis of both viruses by the National Reference Laboratory
for arboviruses (NRLA) from November 2015 to November 2022 are presented. Samples from
655 suspected cases were tested by both molecular and serological assays. Virus and antibody
kinetics, cross-reactivity, and diagnostic performance of IgM ELISA systems were analysed. Of
524 cases tested for DENV, 146 were classified as confirmed, 7 as probable, while 371 were excluded.
Of 619 cases tested for ZIKV, 44 were classified as confirmed, while 492 were excluded. All cases
were imported. Overall, 75.3% (110/146) of DENV and 50% (22/44) of ZIKV cases were confirmed
through direct virus detection methods. High percentages of cross reactivity were observed between
the two viruses. The median lag time from symptoms onset to sample collection was 7 days for both
DENV molecular (range 0–20) and NS1 ELISA (range 0–48) tests, with high percentages of positivity
also after 7 days (39% and 67%, respectively). For ZIKV, the median lag time was 5 days (range 0–22),
with 16% positivity after 7 days. Diagnostic performance was assessed with negative predictive
values ranging from 92% to 95% for the anti-DENV systems, and of 97% for the ZIKV one. Lower
positive predictive values were seen in the tested population (DENV: 55% to 91%, ZIKV: 50%). DENV
and ZIKV diagnosis by molecular test is the gold standard, but sample collection time is a limitation.
Serological tests, including Plaque Reduction Neutralization Test, are thus necessary. Co-circulation
and cross-reactivity between the two viruses increase diagnostic difficulty. Continuous evaluation of
diagnostic strategies is essential to improve laboratory testing
Measurement of the inclusive isolated-photon cross section in pp collisions at √s = 13 TeV using 36 fb−1 of ATLAS data
The differential cross section for isolated-photon production in pp collisions is measured at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC using an integrated luminosity of 36.1 fb. The differential cross section is presented as a function of the photon transverse energy in different regions of photon pseudorapidity. The differential cross section as a function of the absolute value of the photon pseudorapidity is also presented in different regions of photon transverse energy. Next-to-leading-order QCD calculations from Jetphox and Sherpa as well as next-to-next-to-leading-order QCD calculations from Nnlojet are compared with the measurement, using several parameterisations of the proton parton distribution functions. The predictions provide a good description of the data within the experimental and theoretical uncertainties. [Figure not available: see fulltext.
A Kac model for fermions
We introduce a stochastic -particle system and show that, as , an effective description ruled by the homogeneous fermionic
Uehling-Uhlenbeck equation is recovered. The particle model we consider is the
same as the Kac model for the homogeneous Boltzmann equation with an additional
exclusion constraint taking into account the Pauli Exclusion Principle.Comment: 46 page