10,118 research outputs found
GEANT4 : a simulation toolkit
Abstract Geant4 is a toolkit for simulating the passage of particles through matter. It includes a complete range of functionality including tracking, geometry, physics models and hits. The physics processes offered cover a comprehensive range, including electromagnetic, hadronic and optical processes, a large set of long-lived particles, materials and elements, over a wide energy range starting, in some cases, from 250 eV and extending in others to the TeV energy range. It has been designed and constructed to expose the physics models utilised, to handle complex geometries, and to enable its easy adaptation for optimal use in different sets of applications. The toolkit is the result of a worldwide collaboration of physicists and software engineers. It has been created exploiting software engineering and object-oriented technology and implemented in the C++ programming language. It has been used in applications in particle physics, nuclear physics, accelerator design, space engineering and medical physics. PACS: 07.05.Tp; 13; 2
Analog Simulation of Weyl Particles with Cold Atoms
We study theoretically, numerically, and experimentally the relaxation of a
collisionless gas in a quadrupole trap after a momentum kick. The
non-separability of the potential enables a quasi thermalization of the single
particle distribution function even in the absence of interactions.
Suprinsingly, the dynamics features an effective decoupling between the strong
trapping axis and the weak trapping plane. The energy delivered during the kick
is redistributed according to the symmetries of the system and satisfies the
Virial theorem, allowing for the prediction of the final temperatures. We show
that this behaviour is formally equivalent to the relaxation of massless
relativistic Weyl fermions after a sudden displacement from the center of a
harmonic trap
Time-resolved observation of spin-charge deconfinement in fermionic Hubbard chains
Elementary particles such as the electron carry several quantum numbers, for
example, charge and spin. However, in an ensemble of strongly interacting
particles, the emerging degrees of freedom can fundamentally differ from those
of the individual constituents. Paradigmatic examples of this phenomenon are
one-dimensional systems described by independent quasiparticles carrying either
spin (spinon) or charge (holon). Here we report on the dynamical deconfinement
of spin and charge excitations in real space following the removal of a
particle in Fermi-Hubbard chains of ultracold atoms. Using space- and
time-resolved quantum gas microscopy, we track the evolution of the excitations
through their signatures in spin and charge correlations. By evaluating
multi-point correlators, we quantify the spatial separation of the excitations
in the context of fractionalization into single spinons and holons at finite
temperatures
The development and applications of ultrafast electron nanocrystallography
We review the development of ultrafast electron nanocrystallography as a
method for investigating structural dynamics for nanoscale materials and
interfaces. Its sensitivity and resolution are demonstrated in the studies of
surface melting of gold nanocrystals, nonequilibrium transformation of graphite
into reversible diamond-like intermediates, and molecular scale charge
dynamics, showing a versatility for not only determining the structures, but
also the charge and energy redistribution at interfaces. A quantitative scheme
for three-dimensional retrieval of atomic structures is demonstrated with
few-particle (< 1000) sensitivity, establishing this nanocrystallographic
method as a tool for directly visualizing dynamics within isolated
nanomaterials with atomic scale spatio-temporal resolution.Comment: 33 pages, 17 figures (Review article, 2008 conference of ultrafast
electron microscopy conference and ultrafast sciences
GEANT: detector description and simulation tool
As the scale and complexity of High Energy Physics experiments increase, simulation studies require more and more care and become essential to design and optimise the detectors, develop and test the reconstruction and analysis programs, and interpret the experimental data. GEANT is a system of detector description and simulation tools that help physicists in such studies
Visualizing the mobility and distribution of chlorophyll proteins in higher plant thylakoid membranes: effects of photoinhibition and protein phosphorylation
The definitive version is available at www.blackwell-synergy.co
On the excess of ultra-high energy cosmic rays in the direction of Centaurus A
A posteriori anisotropy study of ultra-high energy cosmic rays (UHECRs) with
the Pierre Auger Observatory (PAO) has shown evidence of excess of cosmic ray
particles above 55 EeV within of the direction of the radio galaxy
Centaurus A. However, the origin of the excess remains elusive. We simulate the
propagation of different species of particles coming from the direction of
Centaurus A in the Galactic magnetic fields, and find that only particles of
nuclear charge Z\la 10 can avoid being deflected outside of the
window of Centaurus A. On the other hand, considering the increasingly heavy
composition of UHECRs at the highest energies measured by PAO, a plausible
scenario for cosmic rays from the direction of Centaurus A can be found if they
consist of intermediate-mass nuclei. The chemical composition of cosmic rays
can be further constrained by lower-energy cosmic rays of the same rigidity. We
find that cosmic ray acceleration in the lobes of Centaurus A is not favored,
while acceleration in the stellar winds that are rich in intermediate-mass
nuclei, could meet the requirement. This suggests that the observed excess may
originate from cosmic ray accelerators induced by stellar explosions in the
star-forming regions of Centaurus A and/or the Centaurus cluster located behind
Centaurus A.Comment: 9 pages, 6 figures, 1 table; ApJ accepte
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