11,963 research outputs found
Infinitesimal local operations and differential conditions for entanglement monotones
Much of the theory of entanglement concerns the transformations that are
possible to a state under local operations with classical communication (LOCC);
however, this set of operations is complicated and difficult to describe
mathematically. An idea which has proven very useful is that of the {\it
entanglement monotone}: a function of the state which is invariant under local
unitary transformations and always decreases (or increases) on average after
any local operation. In this paper we look on LOCC as the set of operations
generated by {\it infinitesimal local operations}, operations which can be
performed locally and which leave the state little changed. We show that a
necessary and sufficient condition for a function of the state to be an
entanglement monotone under local operations that do not involve information
loss is that the function be a monotone under infinitesimal local operations.
We then derive necessary and sufficient differential conditions for a function
of the state to be an entanglement monotone. We first derive two conditions for
local operations without information loss, and then show that they can be
extended to more general operations by adding the requirement of {\it
convexity}. We then demonstrate that a number of known entanglement monotones
satisfy these differential criteria. Finally, as an application, we use the
differential conditions to construct a new polynomial entanglement monotone for
three-qubit pure states. It is our hope that this approach will avoid some of
the difficulties in the theory of multipartite and mixed-state entanglement.Comment: 21 pages, RevTeX format, no figures, three minor corrections,
including a factor of two in the differential conditions, the tracelessness
of the matrix in the convexity condition, and the proof that the local purity
is a monotone under local measurements. The conclusions of the paper are
unaffecte
Contains and Inside relationships within combinatorial Pyramids
Irregular pyramids are made of a stack of successively reduced graphs
embedded in the plane. Such pyramids are used within the segmentation framework
to encode a hierarchy of partitions. The different graph models used within the
irregular pyramid framework encode different types of relationships between
regions. This paper compares different graph models used within the irregular
pyramid framework according to a set of relationships between regions. We also
define a new algorithm based on a pyramid of combinatorial maps which allows to
determine if one region contains the other using only local calculus.Comment: 35 page
Irregularity in gamma ray source spectra as a signature of axionlike particles
Oscillations from high energy photons into light pseudoscalar particles in an
external magnetic field are expected to occur in some extensions of the
standard model. It is usually assumed that those axionlike particles (ALPs)
could produce a drop in the energy spectra of gamma ray sources and possibly
decrease the opacity of the Universe for TeV gamma rays. We show here that
these assumptions are in fact based on an average behavior that cannot happen
in real observations of single sources. We propose a new method to search for
photon-ALP oscillations, taking advantage of the fact that a single observation
would deviate from the average expectation. Our method is based on the search
for irregularities in the energy spectra of gamma ray sources. We predict
features that are unlikely to be produced by known astrophysical processes and
a new signature of ALPs that is easily falsifiable.Comment: 6 pages, 3 figures, matches accepted version, improved discussion on
magnetic field models in v
The Architecture of MEG Simulation and Analysis Software
MEG (Mu to Electron Gamma) is an experiment dedicated to search for the
decay that is strongly suppressed in the Standard
Model but predicted in several Super Symmetric extensions of it at an
accessible rate. MEG is a small-size experiment ( physicists at
any time) with a life span of about 10 years. The limited human resource
available, in particular in the core offline group, emphasized the importance
of reusing software and exploiting existing expertise. Great care has been
devoted to provide a simple system that hides implementation details to the
average programmer. That allowed many members of the collaboration to
contribute to the development of the software of the experiment with limited
programming skill. The offline software is based on two frameworks: {\bf REM}
in FORTRAN 77 used for the event generation and detector simulation package
{\bf GEM}, based on GEANT 3, and {\bf ROME} in C++ used in the readout
simulation {\bf Bartender} and in the reconstruction and analysis program {\bf
Analyzer}. Event display in the simulation is based on GEANT 3 graphic
libraries and in the reconstruction on ROOT graphic libraries. Data are stored
in different formats in various stage of the processing. The frameworks include
utilities for input/output, database handling and format conversion transparent
to the user.Comment: Presented at the IEEE NSS Knoxville, 2010 Revised according to
referee's remarks Accepted by European Physical Journal Plu
Platonic crystal with low-frequency locally resonant snail structures. Wave trapping, transmission amplification and shielding
We propose a new type of platonic crystal. The proposed microstructured plate
includes snail resonators with low-frequency resonant vibrations. The
particular dynamic effect of the resonators are highlighted by a comparative
analysis of dispersion properties of homo- geneous and perforated plates.
Analytical and numerical estimates of classes of standing waves are given and
the analysis on a macrocell shows the possibility to obtain localization, wave
trapping and edge waves. Applications include transmission amplification within
two plates separated by a small ligament. Finally we proposed a design
procedure to suppress low frequency flexural vibration in an elongated plate
implementing a by-pass system re- routing waves within the mechanical system.Comment: 11 figures (20 files
Global Dynamics of Subsurface Solar Active Regions
We present three-dimensional numerical simulations of a magnetic loop
evolving in either a convectively stable or unstable rotating shell. The
magnetic loop is introduced in the shell in such a way that it is buoyant only
in a certain portion in longitude, thus creating an \Omega-loop. Due to the
action of magnetic buoyancy, the loop rises and develops asymmetries between
its leading and following legs, creating emerging bipolar regions whose
characteristics are similar to the ones of observed spots at the solar surface.
In particular, we self-consistently reproduce the creation of tongues around
the spot polarities, which can be strongly affected by convection. We moreover
emphasize the presence of ring-shaped magnetic structures around our simulated
emerging regions, which we call "magnetic necklace" and which were seen in a
number of observations without being reported as of today. We show that those
necklaces are markers of vorticity generation at the periphery and below the
rising magnetic loop. We also find that the asymmetry between the two legs of
the loop is crucially dependent on the initial magnetic field strength. The
tilt angle of the emerging regions is also studied in the stable and unstable
cases and seems to be affected both by the convective motions and the presence
of a differential rotation in the convective cases.Comment: 23 pages (ApJ 2-column format), 19 figures, accepted for publication
in Ap
A Method for Determining Cloud-Droplet Impingement on Swept Wings
The general effect of wing sweep on cloud-droplet trajectories about swept wings of high aspect ratio moving at subsonic speeds is discussed. A method of computing droplet trajectories about yawed cylinders and swept wings is presented, and illustrative droplet trajectories are computed. A method of extending two-dimensional calculations of droplet impingement on nonswept wings to swept wings is presented. It is shown that the extent of impingement of cloud droplets on an airfoil surface, the total rate of collection of water, and the local rate of impingement per unit area of airfoil surface can be found for a swept wing from two-dimensional data for a nonswept wing. The impingement on a swept wing is obtained from impingement data for a nonswept airfoil section which is the same as the section in the normal plane of the swept wing by calculating all dimensionless parameters with respect to flow conditions in the normal plane of the swept wing
Variation of Local Liquid-Water Concentration About an Ellipsoid of Fineness Ratio 10 Moving in a Droplet Field
Trajectories of water droplets about an ellipsoid of revolution with a fineness ratio of 10 (10 percent thick) in flight through a droplet field were computed with the aid of a differential analyzer. Analyses of these trajectories indicate that the local concentration of liquid water at various points about an ellipsoid varies considerably and under some conditions may be several times the free-stream concentration. Curves of the local concentration factor as a function of spatial position were obtained and are presented in terms of dimensionless parameters that describe flight and atmospheric conditions. The data indicate that the expected local concentration factors should be considered when choosing the location of devices that protrude into the stream from aircraft fuselages or missiles, or when determining antiicing heat requirements for the protection of these devices
Dirac model of electronic transport in graphene antidot barriers
In order to use graphene for semiconductor applications, such as transistors
with high on/off ratios, a band gap must be introduced into this otherwise
semimetallic material. A promising method of achieving a band gap is by
introducing nanoscale perforations (antidots) in a periodic pattern, known as a
graphene antidot lattice (GAL). A graphene antidot barrier (GAB) can be made by
introducing a 1D GAL strip in an otherwise pristine sheet of graphene. In this
paper, we will use the Dirac equation (DE) with a spatially varying mass term
to calculate the electronic transport through such structures. Our approach is
much more general than previous attempts to use the Dirac equation to calculate
scattering of Dirac electrons on antidots. The advantage of using the DE is
that the computational time is scale invariant and our method may therefore be
used to calculate properties of arbitrarily large structures. We show that the
results of our Dirac model are in quantitative agreement with tight-binding for
hexagonal antidots with armchair edges. Furthermore, for a wide range of
structures, we verify that a relatively narrow GAB, with only a few antidots in
the unit cell, is sufficient to give rise to a transport gap
The H.E.S.S. multi-messenger program
Based on fundamental particle physics processes like the production and
subsequent decay of pions in interactions of high-energy particles, close
connections exist between the acceleration sites of high-energy cosmic rays and
the emission of high-energy gamma rays and high-energy neutrinos. In most cases
these connections provide both spatial and temporal correlations of the
different emitted particles. The combination of the complementary information
provided by these messengers allows to lift ambiguities in the interpretation
of the data and enables novel and highly sensitive analyses. In this
contribution the H.E.S.S. multi-messenger program is introduced and described.
The current core of this newly installed program is the combination of
high-energy neutrinos and high-energy gamma rays. The search for gamma-ray
emission following gravitational wave triggers is also discussed. Furthermore,
the existing program for following triggers in the electromagnetic regime was
extended by the search for gamma-ray emission from Fast Radio Bursts (FRBs). An
overview over current and planned analyses is given and recent results are
presented.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherland
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