4,664 research outputs found
Discontinuous Galerkin methods for solving the acoustic wave equation
In this work we develop a numerical simulator for the propagation of elastic waves by solving the one-dimensional acoustic wave equation with Absorbing Boundary Conditions (ABC’s) on the computational boundaries using Discontinuous Galerkin Finite Element Methods (DGFEM). The DGFEM allows us to easily simulate the presence of a fracture in the elastic medium by means of a linear-slip model. We analize the behaviour of our algorithm by comparing its results against analytic solutions. Furthermore, we show the frequency-dependent effect on the propagation produced by the fracture as appears in previous works. Finally, we present an analysis of the numerical parameters of the method.Fil: Castromán, Gabriel Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas. Departamento de Geofísica Aplicada; ArgentinaFil: Zyserman, Fabio Ivan. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas. Departamento de Geofísica Aplicada; Argentin
Multiple Avalanches Across the Metal-Insulator Transition of Vanadium Oxide Nano-scaled Junctions
The metal insulator transition of nano-scaled devices is drastically
different from the smooth transport curves generally reported. The temperature
driven transition occurs through a series of resistance jumps ranging over 2
decades in amplitude, indicating that the transition is caused by avalanches.
We find a power law distribution of the jump amplitudes, demonstrating an
inherent property of the films. We report a surprising relation between
jump amplitude and device size. A percolation model captures the general
transport behavior, but cannot account for the statistical behavior.Comment: 4 papers and 4 figures submitted to PR
On the transformations generated by the electromagnetic spin and orbital angular momentum operators
We present a study of the properties of the transversal "spin angular
momentum" and "orbital angular momentum" operators. We show that the "spin
angular momentum" operators are generators of spatial translations which depend
on helicity and frequency and that the "orbital angular momentum" operators
generate transformations which are a sequence of this kind of translations and
rotations. We give some examples of the use of these operators in light matter
interaction problems. Their relationship with the helicity operator allows to
involve the electromagnetic duality symmetry in the analysis. We also find that
simultaneous eigenstates of the three "spin" operators and parity define a type
of standing modes which has been recently singled out for the interaction of
light with chiral molecules. With respect to the relationship between "spin
angular momentum", polarization, and total angular momentum, we show that,
except for the case of a single plane wave, the total angular momentum of the
field is decoupled from its vectorial degrees of freedom even in the regime
where the paraxial approximation holds. Finally, we point out a relationship
between the three "spin" operators and the spatial part of the Pauli-Lubanski
four vector
Necessary symmetry conditions for the rotation of light
Two conditions on symmetries are identified as necessary for a linear
scattering system to be able to rotate the linear polarisation of light: Lack
of at least one mirror plane of symmetry and electromagnetic duality symmetry.
Duality symmetry is equivalent to the conservation of the helicity of light in
the same way that rotational symmetry is equivalent to the conservation of
angular momentum. When the system is a solution of a single species of
particles, the lack of at least one mirror plane of symmetry leads to the
familiar requirement of chirality of the individual particle. With respect to
helicity preservation, according to the analytical and numerical evidence
presented in this paper, the solution preserves helicity if and only if the
individual particle itself preserves helicity. However, only in the particular
case of forward scattering the helicity preservation condition on the particle
is relaxed: We show that the random orientation of the molecules endows the
solution with an effective rotational symmetry; at its turn, this leads to
helicity preservation in the forward scattering direction independently of any
property of the particle. This is not the case for a general scattering
direction. These results advance the current understanding of the phenomena of
molecular optical activity and provide insight for the design of polarisation
control devices at the nanoscale.Comment: 17 pages, 3 figure
Far-field measurements of vortex beams interacting with nanoholes
We measure the far-field intensity of vortex beams going through nanoholes.
The process is analyzed in terms of helicity and total angular momentum. It is
seen that the total angular momentum is preserved in the process, and helicity
is not. We compute the ratio between the two transmitted helicity components,
. We observe that this ratio is highly dependent on the helicity
() and the angular momentum () of the incident vortex beam in
consideration. Due to the mirror symmetry of the nanoholes, we are able to
relate the transmission properties of vortex beams with a certain helicity and
angular momentum, with the ones with opposite helicity and angular momentum.
Interestingly, vortex beams enhance the ratio as compared to
those obtained by Gaussian beams
Efficient Environmental Regulation in the Unconventional Oil Industry
US OIL production has skyrocketed since 2007. Technological advances in oil and gas drilling (commonly referred to as ‘fracking’) have allowed producers to access vast petroleum reserves that were previously too costly to recover. The growth in oil and gas production from unconventional sources has been tremendous, so that unconventional sources now make up more than 50 percent of total US petroleum production (EIA 2015). While this represents a boost to job growth and the broader economy, growth in the oil industry comes with its fair share of problems. Academics and news agencies have documented a host of costs associated with new oil and gas production— groundwater pollution, oil spills, large “man camps” and increased crime, and even increases in traffic accidents and exploding train cars. Some of these costs were seen in Iowa with the contentious nature of right-of- Efficient Environmental Regulation in the Unconventional Oil Industry way issues associated with building out the Dakota Access pipeline across the state. Farmers and environmentalists alike are bound together in their concern for right-of-way, human rights concerns, and environmental issues
Slow sedimentation and deformability of charged lipid vesicles
The study of vesicles in suspension is important to understand the
complicated dynamics exhibited by cells in vivo and in vitro. We developed a
computer simulation based on the boundary-integral method to model the three
dimensional gravity-driven sedimentation of charged vesicles towards a flat
surface. The membrane mechanical behavior was modeled using the Helfrich
Hamiltonian and near incompressibility of the membrane was enforced via a model
which accounts for the thermal fluctuations of the membrane. The simulations
were verified and compared to experimental data obtained using suspended
vesicles labelled with a fluorescent probe, which allows visualization using
fluorescence microscopy and confers the membrane with a negative surface
charge. The electrostatic interaction between the vesicle and the surface was
modeled using the linear Derjaguin approximation for a low ionic concentration
solution. The sedimentation rate as a function of the distance of the vesicle
to the surface was determined both experimentally and from the computer
simulations. The gap between the vesicle and the surface, as well as the shape
of the vesicle at equilibrium were also studied. It was determined that
inclusion of the electrostatic interaction is fundamental to accurately predict
the sedimentation rate as the vesicle approaches the surface and the size of
the gap at equilibrium, we also observed that the presence of charge in the
membrane increases its rigidity
Costs of Inefficient Regulation: Evidence from the Bakken
Efficient pollution regulation equalizes marginal abatement costs across sources. Here we study a new flaring regulation in North Dakota\u27s oil and gas industry and document its efficiency. Exploiting detailed well-level data, we find that the regulation reduced flaring 4 to 7 percentage points and accounts for up to half of the observed flaring reductions since 2015. We construct firm-level marginal flaring abatement cost curves and find that the observed flaring reductions could have been achieved at 20%lower cost by imposing a tax on flared gas equal to current public lands royalty rates instead of using firm-specific flaring requirements
Quantum Emulation of Gravitational Waves
Gravitational waves, as predicted by Einstein's general relativity theory,
appear as ripples in the fabric of spacetime traveling at the speed of light.
We prove that the propagation of small amplitude gravitational waves in a
curved spacetime is equivalent to the propagation of a subspace of
electromagnetic states. We use this result to propose the use of entangled
photons to emulate the evolution of gravitational waves in curved spacetimes by
means of experimental electromagnetic setups featuring metamaterials.Comment: 10 pages, 2 figure
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