25,547 research outputs found
Studies of the nucler equation of state using numerical calculations of nuclear drop collisions
A numerical calculation for the full thermal dynamics of colliding nuclei was developed. Preliminary results are reported for the thermal fluid dynamics in such processes as Coulomb scattering, fusion, fusion-fission, bulk oscillations, compression with heating, and collisions of heated nuclei
Causality detection and turbulence in fusion plasmas
This work explores the potential of an information-theoretical causality
detection method for unraveling the relation between fluctuating variables in
complex nonlinear systems. The method is tested on some simple though nonlinear
models, and guidelines for the choice of analysis parameters are established.
Then, measurements from magnetically confined fusion plasmas are analyzed. The
selected data bear relevance to the all-important spontaneous confinement
transitions often observed in fusion plasmas, fundamental for the design of an
economically attractive fusion reactor. It is shown how the present method is
capable of clarifying the interaction between fluctuating quantities such as
the turbulence amplitude, turbulent flux, and Zonal Flow amplitude, and
uncovers several interactions that were missed by traditional methods.Comment: 26 pages, 14 figure
Solcore: A multi-scale, python-based library for modelling solar cells and semiconductor materials
Computational models can provide significant insight into the operation
mechanisms and deficiencies of photovoltaic solar cells. Solcore is a modular
set of computational tools, written in Python 3, for the design and simulation
of photovoltaic solar cells. Calculations can be performed on ideal,
thermodynamic limiting behaviour, through to fitting experimentally accessible
parameters such as dark and light IV curves and luminescence. Uniquely, it
combines a complete semiconductor solver capable of modelling the optical and
electrical properties of a wide range of solar cells, from quantum well devices
to multi-junction solar cells. The model is a multi-scale simulation accounting
for nanoscale phenomena such as the quantum confinement effects of
semiconductor nanostructures, to micron level propagation of light through to
the overall performance of solar arrays, including the modelling of the
spectral irradiance based on atmospheric conditions. In this article we
summarize the capabilities in addition to providing the physical insight and
mathematical formulation behind the software with the purpose of serving as
both a research and teaching tool.Comment: 25 pages, 18 figures, Journal of Computational Electronics (2018
Black Hole Entropy: a spacetime foam approach
The spacetime foam structure is reviewed briefly (topogical fluctuations and
virtual black hole possibility; equation of state of the foam). A model of
space foam at the surface of the event horizon is introduced. The model is
applied to the calculus of the number of states of a black hole, of its entropy
and of other thermodynamical properties. A formula for the number of microholes
on the surface of the event horizon is derived. Thermodynamical properties of
the event horizon are extended to thermodynamical properties of the space. On
the basis of the previous results, the possibility of micro black holes
creation by the Unruh Effect is investigated.Comment: 23 pages, no figures, postscript file gzipped,to be published in
Classical and Quantum Gravity, July 199
Understanding the tsunami with a simple model
In this paper, we use the approximation of shallow water waves (Margaritondo
G 2005 Eur. J. Phys. 26 401) to understand the behaviour of a tsunami in a
variable depth. We deduce the shallow water wave equation and the continuity
equation that must be satisfied when a wave encounters a discontinuity in the
sea depth. A short explanation about how the tsunami hit the west coast of
India is given based on the refraction phenomenon. Our procedure also includes
a simple numerical calculation suitable for undergraduate students in physics
and engineering
Uni-directional transport properties of a serpent billiard
We present a dynamical analysis of a classical billiard chain -- a channel
with parallel semi-circular walls, which can serve as a model for a bended
optical fiber. An interesting feature of this model is the fact that the phase
space separates into two disjoint invariant components corresponding to the
left and right uni-directional motions. Dynamics is decomposed into the jump
map -- a Poincare map between the two ends of a basic cell, and the time
function -- traveling time across a basic cell of a point on a surface of
section. The jump map has a mixed phase space where the relative sizes of the
regular and chaotic components depend on the width of the channel. For a
suitable value of this parameter we can have almost fully chaotic phase space.
We have studied numerically the Lyapunov exponents, time auto-correlation
functions and diffusion of particles along the chain. As a result of a
singularity of the time function we obtain marginally-normal diffusion after we
subtract the average drift. The last result is also supported by some
analytical arguments.Comment: 15 pages, 9 figure (19 .(e)ps files
The multicomponent 2D Toda hierarchy: Discrete flows and string equations
The multicomponent 2D Toda hierarchy is analyzed through a factorization
problem associated to an infinite-dimensional group. A new set of discrete
flows is considered and the corresponding Lax and Zakharov--Shabat equations
are characterized. Reductions of block Toeplitz and Hankel bi-infinite matrix
types are proposed and studied. Orlov--Schulman operators, string equations and
additional symmetries (discrete and continuous) are considered. The
continuous-discrete Lax equations are shown to be equivalent to a factorization
problem as well as to a set of string equations. A congruence method to derive
site independent equations is presented and used to derive equations in the
discrete multicomponent KP sector (and also for its modification) of the theory
as well as dispersive Whitham equations.Comment: 27 pages. In the revised paper we improved the presentatio
Cloud benchmarking and performance analysis of an HPC application in Amazon EC2
Cloud computing platforms have been continuously evolving. Features such as the Elastic Fabric Adapter (EFA) in the Amazon Web Services (AWS) platform have brought yet another revolution in the High Performance Computing (HPC) world, further accelerating the convergence of HPC and cloud computing. Other public clouds also support similar features further fueling this change. In
this paper, we show how and why the performance of a large-scale computational fluid dynamics (CFD) HPC application on AWS competes very closely with the one on Beskow - a Cray XC40 supercomputer at the PDC Center for High-Performance Computing - in terms of cost-efficiency with strong scaling up to 2304 processes. We perform an extensive set of micro and macro bench-
marks in both environments and conduct a comparative analysis. Until as recently as 2020 these benchmarks have notoriously yielded unsatisfactory results for the cloud platforms compared with on-premise infrastructures. Our aim is to access the HPC capabilities of the cloud, and in general to demonstrate how researchers can scale and evaluate the performance of their application in the cloud.ENABL
A trap-based pulsed positron beam optimised for positronium laser spectroscopy
We describe a pulsed positron beam that is optimised for positronium (Ps) laser-spectroscopy experiments. The system is based on a two-stage Surko-type buffer gas trap that produces 4 ns wide pulses containing up to 5 × 105 positrons at a rate of 0.5-10 Hz. By implanting positrons from the trap into a suitable target material, a dilute positronium gas with an initial density of the order of 107 cm−3 is created in vacuum. This is then probed with pulsed (ns) laser systems, where various Ps-laser interactions have been observed via changes in Ps annihilation rates using a fast gamma ray detector. We demonstrate the capabilities of the apparatus and detection methodology via the observation of Rydberg positronium atoms with principal quantum numbers ranging from 11 to 22 and the Stark broadening of the n = 2 → 11 transition in electric fields
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