3,809 research outputs found
Renormalization Group Flow of the Two-Dimensional Hierarchical Coulomb Gas
We consider a quasilinear parabolic differential equation associated with the
renormalization group transformation of the two-dimensional hierarchical
Coulomb system in the limit as the size of the block L goes to 1. We show that
the initial value problem is well defined in a suitable function space and the
solution converges, as t goes to infinity, to one of the countably infinite
equilibrium solutions. The nontrivial equilibrium solution bifurcates from the
trivial one. These solutions are fully described and we provide a complete
analysis of their local and global stability for all values of inverse
temperature. Gallavotti and Nicolo's conjecture on infinite sequence of
``phases transitions'' is also addressed. Our results rule out an intermediate
phase between the plasma and the Kosterlitz-Thouless phases, at least in the
hierarchical model we consider.Comment: 34pages,2figures, to appear in CM
The magnetic exchange parameters and anisotropy of the quasi-two dimensional antiferromagnet NiPS
Neutron inelastic scattering has been used to measure the magnetic
excitations in powdered NiPS, a quasi-two dimensional antiferromagnet with
spin on a honeycomb lattice. The spectra show clear, dispersive magnons
with a meV gap at the Brillouin zone center. The data were fitted
using a Heisenberg Hamiltonian with a single-ion anisotropy assuming no
magnetic exchange between the honeycomb planes. Magnetic exchange interactions
up to the third intraplanar nearest-neighbour were required. The fits show
robustly that NiPS has an easy axis anisotropy with meV and
that the third nearest-neighbour has a strong antiferromagnetic exchange of
meV. The data can be fitted reasonably well with either
or , however the best quantitative agreement with high-resolution data
indicate that the nearest-neighbour interaction is ferromagnetic with meV and that the second nearest-neighbour exchange is small and
antiferromagnetic with meV. The dispersion has a minimum in the
Brillouin zone corner that is slightly larger than that at the Brillouin zone
center, indicating that the magnetic structure of NiPS is close to being
unstable.Comment: 21 pages, 7 figures, 33 reference
Influence of incoherent scattering on stochastic deflection of high-energy negative particle beams in bent crystals
An investigation on stochastic deflection of high-energy negatively charged
particles in a bent crystal was carried out. On the basis of analytical
calculation and numerical simulation it was shown that it exists a maximum
angle at which most of the beam is deflected. The existence of a maximum, which
is taken in the correspondence of the optimal radius of curvature, is a novelty
with respect to the case of positively charged particles, for which the
deflection angle can be freely increased by increasing the crystal length. This
difference has to be ascribed to the stronger contribution of incoherent
scattering affecting the dynamics of negative particles that move closer to
atomic nuclei and electrons. We therefore identified the ideal parameters for
the exploitation of axial confinement for negatively charged particle beam
manipulation in future high-energy accelerators, e.g., ILC or muon colliders
Reasoning About a Service-oriented Programming Paradigm
This paper is about a new way for programming distributed applications: the
service-oriented one. It is a concept paper based upon our experience in
developing a theory and a language for programming services. Both the
theoretical formalization and the language interpreter showed us the evidence
that a new programming paradigm exists. In this paper we illustrate the basic
features it is characterized by
Low-latency analysis pipeline for compact binary coalescences in the advanced gravitational wave detector era
The multi-band template analysis (MBTA) pipeline is a low-latency coincident
analysis pipeline for the detection of gravitational waves (GWs) from compact
binary coalescences. MBTA runs with a low computational cost, and can identify
candidate GW events online with a sub-minute latency. The low computational
running cost of MBTA also makes it useful for data quality studies. Events
detected by MBTA online can be used to alert astronomical partners for
electromagnetic follow-up. We outline the current status of MBTA and give
details of recent pipeline upgrades and validation tests that were performed in
preparation for the first advanced detector observing period. The MBTA pipeline
is ready for the outset of the advanced detector era and the exciting prospects
it will bring.Comment: 18 pages, 10 figure
Principali tecniche e strumenti per il rilievo tridimensionale in ambito archeologico
The increase of 3D acquisition and modeling techniques applied to archeology is due principally to (i) their capacity to survey archeological artifacts with high precision and a non-contact approach and (ii) the possibility to create 3D digital models useful for data analysis, simulation and preservation. These benefits in terms of knowledge oblige the contemporary archaeologist to acquire a better understanding of 3D acquisition and modeling principles and practice. This evidence arises from the necessity of adopting a common language for experts in 3D data management and archaeologists with the principal aim being the understanding of each other’s requirements and sharing of the purposes of the project. In this article the authors propose a concise but exhaustive explanation of the working principles of active and passive 3D acquisition techniques. For each one a description of instruments and methodologies is developed, pointing out pros and cons of every technique. In conclusion, a sensor fusion approach is presented as an interesting solution to increase the instrument performances while obtaining at the same time a quality improvement of 3D acquisition and modeling results. A final multi-resolution application about Pompeii Forum 3D modeling follows and closes the article
- …