3,841 research outputs found
Geant4 based simulation of the Water Cherenkov Detectors of the LAGO Project
To characterize the signals registered by the different types of water
Cherenkov detectors (WCD) used by the Latin American Giant Observatory (LAGO)
Project, it is necessary to develop detailed simulations of the detector
response to the flux of secondary particles at the detector level. These
particles are originated during the interaction of cosmic rays with the
atmosphere. In this context, the LAGO project aims to study the high energy
component of gamma rays bursts (GRBs) and space weather phenomena by looking
for the solar modulation of galactic cosmic rays (GCRs). Focus in this, a
complete and complex chain of simulations is being developed that account for
geomagnetic effects, atmospheric reaction and detector response at each LAGO
site. In this work we shown the first steps of a GEANT4 based simulation for
the LAGO WCD, with emphasis on the induced effects of the detector internal
diffusive coating.Comment: 5 pages, 4 figures, Proceedings X SILAFAE Medellin-2014. To appear in
Nuclear Physics B - Proceedings Supplement
Electron gas at the interface between two antiferromagnetic insulating manganites
We study theoretically the magnetic and electric properties of the interface
between two antiferromagnetic and insulating manganites: La0.5Ca0.5MnO3, a
strong correlated insulator, and CaMnO3, a band-insulator. We find that a
ferromagnetic and metallic electron gas is formed at the interface between the
two layers. We confirm the metallic character of the interface by calculating
the in-plane conductance. The possibility of increasing the electron gas
density by selective doping is also discussed.Comment: 6 pages, including 9 figure
Theory of one and two donors in Silicon
We provide here a roadmap for modeling silicon nano-devices with one or two
group V donors (D). We discuss systems containing one or two electrons, that
is, D^0, D^-, D_2^+ and D_2^0 centers. The impact of different levels of
approximation is discussed. The most accurate instances -- for which we provide
quantitative results -- are within multivalley effective mass including the
central cell correction and a configuration interaction account of the
electron-electron correlations. We also derive insightful, yet less accurate,
analytical approximations and discuss their validity and limitations -- in
particular, for a donor pair, we discuss the single orbital LCAO method, the
Huckel approximation and the Hubbard model. Finally we discuss the connection
between these results and recent experiments on few dopant devices.Comment: 13 pages, 6 figure
Effect of strain on the orbital and magnetic ordering of manganite thin films and their interface with an insulator
We study the effect of uniform uniaxial strain on the ground state electronic
configuration of a thin film manganite. Our model Hamiltonian includes the
double-exchange, the Jahn-Teller electron-lattice coupling, and the
antiferromagnetic superexchange. The strain arises due to the lattice mismatch
between an insulating substrate and a manganite which produces a tetragonal
distortion. This is included in the model via a modification of the hopping
amplitude and the introduction of an energy splitting between the Mn e_g
levels. We analyze the bulk properties of half-doped manganites and the
electronic reconstruction at the interface between a ferromagnetic and metallic
manganite and the insulating substrate. The strain drives an orbital selection
modifying the electronic properties and the magnetic ordering of manganites and
their interfaces.Comment: 8 pages, 8 figure
Dynamical description of the buildup process in resonant tunneling: Evidence of exponential and non-exponential contributions
The buildup process of the probability density inside the quantum well of a
double-barrier resonant structure is studied by considering the analytic
solution of the time dependent Schr\"{o}dinger equation with the initial
condition of a cutoff plane wave. For one level systems at resonance condition
we show that the buildup of the probability density obeys a simple charging up
law, where is the
stationary wave function and the transient time constant is exactly
two lifetimes. We illustrate that the above formula holds both for symmetrical
and asymmetrical potential profiles with typical parameters, and even for
incidence at different resonance energies. Theoretical evidence of a crossover
to non-exponential buildup is also discussed.Comment: 4 pages, 2 figure
Algebraic computation of some intersection D-modules
Let be a complex analytic manifold, a locally
quasi-homogeneous free divisor, an integrable logarithmic connection with
respect to and the local system of the horizontal sections of on
. In this paper we give an algebraic description in terms of of the
regular holonomic D-module whose de Rham complex is the intersection complex
associated with . As an application, we perform some effective computations
in the case of quasi-homogeneous plane curves.Comment: 18 page
Impact of the valley degree of freedom on the control of donor electrons near a Si/SiO_2 interface
We analyze the valley composition of one electron bound to a shallow donor
close to a Si/barrier interface as a function of an applied electric field. A
full six-valley effective mass model Hamiltonian is adopted. For low fields,
the electron ground state is essentially confined at the donor. At high fields
the ground state is such that the electron is drawn to the interface, leaving
the donor practically ionized. Valley splitting at the interface occurs due to
the valley-orbit coupling, V_vo^I = |V_vo^I| e^{i theta}. At intermediate
electric fields, close to a characteristic shuttling field, the electron states
may constitute hybridized states with valley compositions different from the
donor and the interface ground states. The full spectrum of energy levels shows
crossings and anti-crossings as the field varies. The degree of level
repulsion, thus the width of the anti-crossing gap, depends on the relative
valley compositions, which vary with |V_vo^I|, theta and the interface-donor
distance. We focus on the valley configurations of the states involved in the
donor-interface tunneling process, given by the anti-crossing of the three
lowest eigenstates. A sequence of two anti-crossings takes place and the
complex phase theta affects the symmetries of the eigenstates and level
anti-crossing gaps. We discuss the implications of our results on the practical
manipulation of donor electrons in Si nanostructures.Comment: 8 pages, including 5 figures. v2: Minor clarifying changes in the
text and figures. Change of title. As published in PR
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