13,733 research outputs found
Imaging stress and magnetism at high pressures using a nanoscale quantum sensor
Pressure alters the physical, chemical and electronic properties of matter.
The development of the diamond anvil cell (DAC) enables tabletop experiments to
investigate a diverse landscape of high-pressure phenomena ranging from the
properties of planetary interiors to transitions between quantum mechanical
phases. In this work, we introduce and utilize a novel nanoscale sensing
platform, which integrates nitrogen-vacancy (NV) color centers directly into
the culet (tip) of diamond anvils. We demonstrate the versatility of this
platform by performing diffraction-limited imaging (~600 nm) of both stress
fields and magnetism, up to pressures ~30 GPa and for temperatures ranging from
25-340 K. For the former, we quantify all six (normal and shear) stress
components with accuracy GPa, offering unique new capabilities for
characterizing the strength and effective viscosity of solids and fluids under
pressure. For the latter, we demonstrate vector magnetic field imaging with
dipole accuracy emu, enabling us to measure the pressure-driven
phase transition in iron as well as the complex
pressure-temperature phase diagram of gadolinium. In addition to DC vector
magnetometry, we highlight a complementary NV-sensing modality using T1 noise
spectroscopy; crucially, this demonstrates our ability to characterize phase
transitions even in the absence of static magnetic signatures. By integrating
an atomic-scale sensor directly into DACs, our platform enables the in situ
imaging of elastic, electric and magnetic phenomena at high pressures.Comment: 18 + 50 pages, 4 + 19 figure
A Multi-Grid Iterative Method for Photoacoustic Tomography
Inspired by the recent advances on minimizing nonsmooth or bound-constrained
convex functions on models using varying degrees of fidelity, we propose a line
search multigrid (MG) method for full-wave iterative image reconstruction in
photoacoustic tomography (PAT) in heterogeneous media. To compute the search
direction at each iteration, we decide between the gradient at the target
level, or alternatively an approximate error correction at a coarser level,
relying on some predefined criteria. To incorporate absorption and dispersion,
we derive the analytical adjoint directly from the first-order acoustic wave
system. The effectiveness of the proposed method is tested on a total-variation
penalized Iterative Shrinkage Thresholding algorithm (ISTA) and its accelerated
variant (FISTA), which have been used in many studies of image reconstruction
in PAT. The results show the great potential of the proposed method in
improving speed of iterative image reconstruction
Transient External 3D Excitation of a Dispersive and Antisotropic Slab
Propagation of a transient electromagnetic field in a stratified, dispersive and anisotropic slab and related direct and inverse problems are investigated. The field is generated by a transient external 3D source. The analysis relies on the wave splitting concept and a two-dimensional Fourier transformation in the transverse spatial coordinates. An investigation of the physical properties of the split fields is made. To solve the direct and inverse scattering problems, wave propagators are used. This method is a generalization and a unification of the previously used imbedding and Green functions methods. The wave propagator approach provides an exact solution of the transmission operator. From this solution it is possible to extract the first precursor (the Sommerfeld forerunner). These results also hold for a bi-anisotropic slab. An inverse problem is outlined using reflection and transmission data corresponding to four, two-dimensional Fourier parameters. Due to the stratification of the medium, the inverse Fourier transformation is not needed in the inverse problem
Wave propagators for transient waves in one-dimensional media
Wave propagators are introduced for transient wave propagation in a general one-dimensional medium. The definition of wave propagators is based upon a wave splitting technique. Several properties for the propagators are given and the relations between the method of propagators and the invariant imbedding method and the Green function approach are discussed
Fornax: a Flexible Code for Multiphysics Astrophysical Simulations
This paper describes the design and implementation of our new multi-group,
multi-dimensional radiation hydrodynamics (RHD) code Fornax and provides a
suite of code tests to validate its application in a wide range of physical
regimes. Instead of focusing exclusively on tests of neutrino radiation
hydrodynamics relevant to the core-collapse supernova problem for which Fornax
is primarily intended, we present here classical and rigorous demonstrations of
code performance relevant to a broad range of multi-dimensional hydrodynamic
and multi-group radiation hydrodynamic problems. Our code solves the
comoving-frame radiation moment equations using the M1 closure, utilizes
conservative high-order reconstruction, employs semi-explicit matter and
radiation transport via a high-order time stepping scheme, and is suitable for
application to a wide range of astrophysical problems. To this end, we first
describe the philosophy, algorithms, and methodologies of Fornax and then
perform numerous stringent code tests, that collectively and vigorously
exercise the code, demonstrate the excellent numerical fidelity with which it
captures the many physical effects of radiation hydrodynamics, and show
excellent strong scaling well above 100k MPI tasks.Comment: Accepted to the Astrophysical Journal Supplement Series; A few more
textual and reference updates; As before, one additional code test include
Lorentz breaking Effective Field Theory and observational tests
Analogue models of gravity have provided an experimentally realizable test
field for our ideas on quantum field theory in curved spacetimes but they have
also inspired the investigation of possible departures from exact Lorentz
invariance at microscopic scales. In this role they have joined, and sometime
anticipated, several quantum gravity models characterized by Lorentz breaking
phenomenology. A crucial difference between these speculations and other ones
associated to quantum gravity scenarios, is the possibility to carry out
observational and experimental tests which have nowadays led to a broad range
of constraints on departures from Lorentz invariance. We shall review here the
effective field theory approach to Lorentz breaking in the matter sector,
present the constraints provided by the available observations and finally
discuss the implications of the persisting uncertainty on the composition of
the ultra high energy cosmic rays for the constraints on the higher order,
analogue gravity inspired, Lorentz violations.Comment: 47 pages, 4 figures. Lecture Notes for the IX SIGRAV School on
"Analogue Gravity", Como (Italy), May 2011. V.3. Typo corrected, references
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