1,272 research outputs found
Efficient grid-based method in nonequilibrium Green's function calculations. Application to model atoms and molecules
We propose and apply the finite-element discrete variable representation to
express the nonequilibrium Green's function for strongly inhomogeneous quantum
systems. This method is highly favorable against a general basis approach with
regard to numerical complexity, memory resources, and computation time. Its
flexibility also allows for an accurate representation of spatially extended
hamiltonians, and thus opens the way towards a direct solution of the two-time
Schwinger/Keldysh/Kadanoff-Baym equations on spatial grids, including e.g. the
description of highly excited states in atoms. As first benchmarks, we compute
and characterize, in Hartree-Fock and second Born approximation, the ground
states of the He atom, the H molecule and the LiH molecule in one spatial
dimension. Thereby, the ground-state/binding energies, densities and
bond-lengths are compared with the direct solution of the time-dependent
Schr\"odinger equation.Comment: 11 pages, 5 figures, submitted to Physical Review
The H.E.S.S. II GRB Program
Gamma-ray bursts (GRBs) are some of the most energetic and exotic events in
the Universe, however their behaviour at the highest energies (>10 GeV) is
largely unknown. Although the Fermi-LAT space telescope has detected several
GRBs in this energy range, it is limited by the relatively small collection
area of the instrument. The H.E.S.S. experiment has now entered its second
phase by adding a fifth telescope of 600 m mirror area to the centre of
the array. This new telescope increases the energy range of the array, allowing
it to probe the sub-100 GeV range while maintaining the large collection area
of ground based gamma-ray observatories, essential to probing short-term
variability at these energies. We will present a description of the GRB
observation scheme used by the H.E.S.S. experiment, summarising the behaviour
and performance of the rapid GRB repointing system, the conditions under which
potential GRB repointings are made and the data analysis scheme used for these
observations.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherland
A Comprehensive Survey of Brane Tilings
An infinite class of gauge theories can be engineered on
the worldvolume of D3-branes probing toric Calabi-Yau 3-folds. This kind of
setup has multiple applications, ranging from the gauge/gravity correspondence
to local model building in string phenomenology. Brane tilings fully encode the
gauge theories on the D3-branes and have substantially simplified their
connection to the probed geometries. The purpose of this paper is to push the
boundaries of computation and to produce as comprehensive a database of brane
tilings as possible. We develop efficient implementations of brane tiling tools
particularly suited for this search. We present the first complete
classification of toric Calabi-Yau 3-folds with toric diagrams up to area 8 and
the corresponding brane tilings. This classification is of interest to both
physicists and mathematicians alike.Comment: 39 pages. Link to Mathematica modules provide
Nonequilibrium properties of strongly correlated artificial atoms - a Green's functions approach
A nonequilibrium Green's functions (NEGF) approach for spatially
inhomogeneous, strongly correlated artificial atoms is presented and applied to
compute the time-dependent properties while starting from a (correlated)
initial few-electron state at finite temperatures. In the regime of moderate to
strong coupling, we consider the Kohn mode of a three-electron system in a
parabolic confinement excited by a short pulsed classical laser field treated
in dipole approximation. In particular, we numerically confirm that this mode
is preserved within a conserving (e.g. Hartree-Fock or second Born) theory
First order Mott transition at zero temperature in two dimensions: Variational plaquette study
The nature of the metal-insulator Mott transition at zero temperature has
been discussed for a number of years. Whether it occurs through a quantum
critical point or through a first order transition is expected to profoundly
influence the nature of the finite temperature phase diagram. In this paper, we
study the zero temperature Mott transition in the two-dimensional Hubbard model
on the square lattice with the variational cluster approximation. This takes
into account the influence of antiferromagnetic short-range correlations. By
contrast to single-site dynamical mean-field theory, the transition turns out
to be first order even at zero temperature.Comment: 6 pages, 5 figures, version 2 with additional results for 8 bath
site
Pairing of charged particles in a quantum plasmoid
We study a quantum spherically symmetric object which is based on radial
plasma oscillations. Such a plasmoid is supposed to exist in a dense plasma
containing electrons, ions, and neutral particles. The method of creation and
annihilation operators is applied to quantize the motion of charged particles
in a self-consistent potential. We also study the effective interaction between
oscillating particles owing to the exchange of a virtual acoustic wave, which
is excited in the neutral component of plasma. It is shown that this
interaction can be attractive and result in the formation of ion pairs. We
discuss possible applications of this phenomenon in astrophysical and
terrestrial plasmas.Comment: 17 pages, no figures, two columns, LaTeX2e; paper was significantly
revised; title was changed; 16 new references were included; the discussion
on ion-acoustic waves was added to Sec. 2; Secs. 3 and 4 were shortened; a
more detailed discussion was added to Sec. 7; accepted for publication to
J.Phys.
Optimization of an Alkylpolyglucoside-Based Dishwashing Detergent Formulation.
The aim of this work was to formulate and optimize the washing performance of an alkylpolyglucoside-based dishwashing detergent. The liquid detergent was formulated with five ingredients of commercial origin: anionic (linear sodium alkylbenzenesulfonate and sodium laurylethersulfate), nonionic (C12–C14 alkylpolyglucoside) and zwitterionic (a fatty acid amide derivative with a betaine structure) surfactants, and NaCl for viscosity control. In addition to the plate test, other properties were investigated including ‘‘cloud point’’, viscosity, and emulsion stability. Statistical analysis software was used to generate a central composite experimental design. Then, a second order design and analysis of experiments approach, known as the Response Surface Methodology, was set up to investigate the effects of the five components of the formulation on the studied properties in the region covering plausible component ranges. The method proved to be efficient for locating the domains of concentrations where the desired properties were met
The first GCT camera for the Cherenkov Telescope Array
The Gamma Cherenkov Telescope (GCT) is proposed to be part of the Small Size
Telescope (SST) array of the Cherenkov Telescope Array (CTA). The GCT
dual-mirror optical design allows the use of a compact camera of diameter
roughly 0.4 m. The curved focal plane is equipped with 2048 pixels of
~0.2{\deg} angular size, resulting in a field of view of ~9{\deg}. The GCT
camera is designed to record the flashes of Cherenkov light from
electromagnetic cascades, which last only a few tens of nanoseconds. Modules
based on custom ASICs provide the required fast electronics, facilitating
sampling and digitisation as well as first level of triggering. The first GCT
camera prototype is currently being commissioned in the UK. On-telescope tests
are planned later this year. Here we give a detailed description of the camera
prototype and present recent progress with testing and commissioning.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
A New Linear Logic for Deadlock-Free Session-Typed Processes
The π -calculus, viewed as a core concurrent programming language, has been used as the target of much research on type systems for concurrency. In this paper we propose a new type system for deadlock-free session-typed π -calculus processes, by integrating two separate lines of work. The first is the propositions-as-types approach by Caires and Pfenning, which provides a linear logic foundation for session types and guarantees deadlock-freedom by forbidding cyclic process connections. The second is Kobayashi’s approach in which types are annotated with priorities so that the type system can check whether or not processes contain genuine cyclic dependencies between communication operations. We combine these two techniques for the first time, and define a new and more expressive variant of classical linear logic with a proof assignment that gives a session type system with Kobayashi-style priorities. This can be seen in three ways: (i) as a new linear logic in which cyclic structures can be derived and a CYCLE -elimination theorem generalises CUT -elimination; (ii) as a logically-based session type system, which is more expressive than Caires and Pfenning’s; (iii) as a logical foundation for Kobayashi’s system, bringing it into the sphere of the propositions-as-types paradigm
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