12,688 research outputs found
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
THE CAVES Project - Collaborative Analysis Versioning Environment System; THE CODESH Project - Collaborative Development Shell
A key feature of collaboration in science and software development is to have
a {\em log} of what and how is being done - for private use and reuse and for
sharing selected parts with collaborators, which most often today are
distributed geographically on an ever larger scale. Even better if this log is
{\em automatic}, created on the fly while a scientist or software developer is
working in a habitual way, without the need for extra efforts. The {\tt CAVES}
and {\tt CODESH} projects address this problem in a novel way, building on the
concepts of {\em virtual state} and {\em virtual transition} to provide an
automatic persistent logbook for sessions of data analysis or software
development in a collaborating group. A repository of sessions can be
configured dynamically to record and make available the knowledge accumulated
in the course of a scientific or software endeavor. Access can be controlled to
define logbooks of private sessions and sessions shared within or between
collaborating groups.Comment: 4 pages, presented at the Meeting of the Division of Particles and
Fields of the APS, Riverside, USA, August 200
Novel String Banana Template Method of Track Reconstruction for high Multiplicity Events with Significant Multiple Scattering
Novel String Banana Template Method (SBTM) for track reconstruction in high
multiplicity events in non-uniform magnetic field spectrometer with emphasis on
the lowest momenta tracks with significant Multiple Scattering (MS) is
described. Two steps model of track with additional parameter/s which takes
into account MS for this particular track is introduced. SBTM is time efficient
and demonstrates better resolutions than another method equivalent to the Least
Squares method (LSM).Comment: 3 pages, 3 figures, DPF2004 Proceeding, International Journal of
Modern Physics
Extra Shared Entanglement Reduces Memory Demand in Quantum Convolutional Coding
We show how extra entanglement shared between sender and receiver reduces the
memory requirements for a general entanglement-assisted quantum convolutional
code. We construct quantum convolutional codes with good error-correcting
properties by exploiting the error-correcting properties of an arbitrary basic
set of Pauli generators. The main benefit of this particular construction is
that there is no need to increase the frame size of the code when extra shared
entanglement is available. Then there is no need to increase the memory
requirements or circuit complexity of the code because the frame size of the
code is directly related to these two code properties. Another benefit, similar
to results of previous work in entanglement-assisted convolutional coding, is
that we can import an arbitrary classical quaternary code for use as an
entanglement-assisted quantum convolutional code. The rate and error-correcting
properties of the imported classical code translate to the quantum code. We
provide an example that illustrates how to import a classical quaternary code
for use as an entanglement-assisted quantum convolutional code. We finally show
how to "piggyback" classical information to make use of the extra shared
entanglement in the code.Comment: 7 pages, 1 figure, accepted for publication in Physical Review
Impingement of Cloud Droplets on 36.5-Percent-Thick Joukowski Airfoil at Zero Angle of Attack and Discussion of Use as Cloud Measuring Instrument in Dye-Tracer Technique
The trajectories of droplets i n the air flowing past a 36.5-percent-thick Joukowski airfoil at zero angle of attack were determined. The amount of water i n droplet form impinging on the airfoil, the area of droplet impingement, and the rate of droplet impingement per unit area on the airfoil surface were calculated from the trajectories and cover a large range of flight and atmospheric conditions. With the detailed impingement information available, the 36.5-percent-thick Joukowski airfoil can serve the dual purpose of use as the principal element in instruments for making measurements in clouds and of a basic shape for estimating impingement on a thick streamlined body. Methods and examples are presented for illustrating some limitations when the airfoil is used as the principal element in the dye-tracer technique
Quantum state diffusion with a moving basis: computing quantum-optical spectra
Quantum state diffusion (QSD) as a tool to solve quantum-optical master
equations by stochastic simulation can be made several orders of magnitude more
efficient if states in Hilbert space are represented in a moving basis of
excited coherent states. The large savings in computer memory and time are due
to the localization property of the QSD equation. We show how the method can be
used to compute spectra and give an application to second harmonic generation.Comment: 8 pages in RevTeX, 1 uuencoded postscript figure, submitted to Phys.
Rev.
Quantum state diffusion, localization and computation
Numerical simulation of individual open quantum systems has proven advantages
over density operator computations. Quantum state diffusion with a moving basis
(MQSD) provides a practical numerical simulation method which takes full
advantage of the localization of quantum states into wave packets occupying
small regions of classical phase space. Following and extending the original
proposal of Percival, Alber and Steimle, we show that MQSD can provide a
further gain over ordinary QSD and other quantum trajectory methods of many
orders of magnitude in computational space and time. Because of these gains, it
is even possible to calculate an open quantum system trajectory when the
corresponding isolated system is intractable. MQSD is particularly advantageous
where classical or semiclassical dynamics provides an adequate qualitative
picture but is numerically inaccurate because of significant quantum effects.
The principles are illustrated by computations for the quantum Duffing
oscillator and for second harmonic generation in quantum optics. Potential
applications in atomic and molecular dynamics, quantum circuits and quantum
computation are suggested.Comment: 16 pages in LaTeX, 2 uuencoded postscript figures, submitted to J.
Phys.
Soft X-ray emission in kink-unstable coronal loops
Solar flares are associated with intense soft X-ray emission generated by the
hot flaring plasma. Kink unstable twisted flux-ropes provide a source of
magnetic energy which can be released impulsively and account for the flare
plasma heating. We compute the temporal evolution of the thermal X-ray emission
in kink-unstable coronal loops using MHD simulations and discuss the results of
with respect to solar flare observations. The model consists of a highly
twisted loop embedded in a region of uniform and untwisted coronal magnetic
field. We let the kink instability develop, compute the evolution of the plasma
properties in the loop (density, temperature) without accounting for mass
exchange with the chromosphere. We then deduce the X-ray emission properties of
the plasma during the whole flaring episode. During the initial phase of the
instability plasma heating is mostly adiabatic. Ohmic diffusion takes over as
the instability saturates, leading to strong and impulsive heating (> 20 MK),
to a quick enhancement of X-ray emission and to the hardening of the thermal
X-ray spectrum. The temperature distribution of the plasma becomes broad, with
the emission measure depending strongly on temperature. Significant emission
measures arise for plasma at temperatures T > 9 MK. The magnetic flux-rope then
relaxes progressively towards a lower energy state as it reconnects with the
background flux. The loop plasma suffers smaller sporadic heating events but
cools down conductively. The total thermal X-ray emission slowly fades away
during this phase, and the high temperature component of emission measure
distribution converges to the power-law distribution . The
amount of twist deduced directly from the X-ray emission patterns is
considerably lower than the maximum magnetic twist in the simulated flux-ropes.Comment: submitted to A&
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
Flux-tube geometry and solar wind speed during an activity cycle
The solar wind speed at 1 AU shows variations in latitude and in time which
reflect the evolution of the global background magnetic field during the
activity cycle. It is commonly accepted that the terminal wind speed in a
magnetic flux-tube is anti-correlated with its expansion ratio, which motivated
the definition of widely-used semi-empirical scaling laws relating one to the
other. In practice, such scaling laws require ad-hoc corrections. A predictive
law based solely on physical principles is still missing. We test whether the
flux-tube expansion is the controlling factor of the wind speed at all phases
of the cycle and at all latitudes using a very large sample of wind-carrying
open magnetic flux-tubes. We furthermore search for additional physical
parameters based on the geometry of the coronal magnetic field which have an
influence on the terminal wind flow speed. We use MHD simulations of the corona
and wind coupled to a dynamo model to provide a large statistical ensemble of
open flux-tubes which we analyse conjointly in order to identify relations of
dependence between the wind speed and geometrical parameters of the flux-tubes
which are valid globally (for all latitudes and moments of the cycle). Our
study confirms that the terminal speed of the solar wind depends very strongly
on the geometry of the open magnetic flux-tubes through which it flows. The
total flux-tube expansion is more clearly anti-correlated with the wind speed
for fast rather than for slow wind flows, and effectively controls the
locations of these flows during solar minima. Overall, the actual asymptotic
wind speeds attained are also strongly dependent on field-line inclination and
magnetic field amplitude at the foot-points. We suggest ways of including these
parameters on future predictive scaling-laws for the solar wind speed.Comment: Accepted for publicaton on Astronomy & Astrophysic
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