60,086 research outputs found
Baryonic Signatures in Large-Scale Structure
We investigate the consequences of a non-negligible baryon fraction for
models of structure formation in Cold Dark Matter dominated cosmologies,
emphasizing in particular the existence of oscillations in the present-day
matter power spectrum. These oscillations are the remnants of acoustic
oscillations in the photon-baryon fluid before last scattering. For acceptable
values of the cosmological and baryon densities, the oscillations modulate the
power by up to 10%, with a `period' in spatial wavenumber which is close to
Delta k approximately 0.05/ Mpc. We study the effects of nonlinear evolution on
these features, and show that they are erased for k > 0.2 h/ Mpc. At larger
scales, the features evolve as expected from second-order perturbation theory:
the visibility of the oscillations is affected only weakly by nonlinear
evolution. No realistic CDM parameter combination is able to account for the
claimed feature near k = 0.1 h/ Mpc in the APM power spectrum, or the excess
power at 100 Mpc/h wavelengths quoted by several recent surveys. Thus baryonic
oscillations are not predicted to dominate existing measurements of clustering.
We examine several effects which may mask the features which are predicted, and
conclude that future galaxy surveys may be able to detect the oscillatory
features in the power spectrum provided baryons comprise more than 15% of the
total density, but that it will be a technically challenging achievement.Comment: 16 pages, 13 Figures, to be published in MNRA
Destruction of the Mott Insulating Ground State of Ca_2RuO_4 by a Structural Transition
We report a first-order phase transition at T_M=357 K in single crystal
Ca_2RuO_4, an isomorph to the superconductor Sr_2RuO_4. The discontinuous
decrease in electrical resistivity signals the near destruction of the Mott
insulating phase and is triggered by a structural transition from the low
temperature orthorhombic to a high temperature tetragonal phase. The magnetic
susceptibility, which is temperature dependent but not Curie-like decreases
abruptly at TM and becomes less temperature dependent. Unlike most insulator to
metal transitions, the system is not magnetically ordered in either phase,
though the Mott insulator phase is antiferromagnetic below T_N=110 K.Comment: Accepted for publication in Phys. Rev. B (Rapid Communications
Inverse Design of Perfectly Transmitting Eigenchannels in Scattering Media
Light-matter interactions inside turbid medium can be controlled by tailoring
the spatial distribution of energy density throughout the system. Wavefront
shaping allows selective coupling of incident light to different transmission
eigenchannels, producing dramatically different spatial intensity profiles. In
contrast to the density of transmission eigenvalues that is dictated by the
universal bimodal distribution, the spatial structures of the eigenchannels are
not universal and depend on the confinement geometry of the system. Here, we
develop and verify a model for the transmission eigenchannel with the
corresponding eigenvalue close to unity. By projecting the original problem of
two-dimensional diffusion in a homogeneous scattering medium onto a
one-dimensional inhomogeneous diffusion, we obtain an analytical expression
relating the intensity profile to the shape of the confining waveguide.
Inverting this relationship enables the inverse design of the waveguide shape
to achieve the desired energy distribution for the perfectly transmitting
eigenchannel. Our approach also allows to predict the intensity profile of such
channel in a disordered slab with open boundaries, pointing to the possibility
of controllable delivery of light to different depths with local illumination.Comment: 9 pages, 6 figure
Numerical and experimental assessment of the modal curvature method for damage detection in plate structures
This paper is concerned with the use of numerically obtained modal curvatures for damage detection in both isotropic and composite laminated plates. Numerical simulations are carried out by using COMSOL Multiphysics as FEM solver of the governing equations, in which a Mindlin-Reissner plate model is assumed and defects are introduced as localized smoothed variations of the baseline (healthy) configuration. Experiments are also performed on steel and aluminum plates using scanning laser vibrometry. This study confirms that the central difference method greatly amplifies the measurement errors and its application leads to ineffective predictions for damage detection, even after denoising. As a consequence, different numerical techniques should be explored to allow the use of numerically obtained modal curvatures for structural health monitoring. Herein, the Savitzky-Golay filter (or least-square smoothing filter) is considered for the numerical differentiation of noisy data
Critical States Embedded in the Continuum
We introduce a class of critical states which are embedded in the continuum
(CSC) of one-dimensional optical waveguide array with one non-Hermitian defect.
These states are at the verge of being fractal and have real propagation
constant. They emerge at a phase transition which is driven by the imaginary
refractive index of the defect waveguide and it is accompanied by a mode
segregation which reveals analogies with the Dicke super -radiance. Below this
point the states are extended while above they evolve to exponentially
localized modes. An addition of a background gain or loss can turn these
localized states to bound states in the continuum.Comment: 4.5 pages, 3 figures, 1 page of supplementary material including one
figur
Competing Ground States in Triple-layered Sr4Ru3O10: Verging on Itinerant Ferromagnetism with Critical Fluctuations
Sr4Ru3O10 is characterized by a sharp metamagnetic transition and
ferromagnetic behavior occurring within the basal plane and along the c-axis,
respectively. Resistivity at magnetic field, B, exhibits low-frequency quantum
oscillations when B||c-axis and large magnetoresistivity accompanied by
critical fluctuations driven by the metamagnetism when B^c-axis. The complex
behavior evidenced in resistivity, magnetization and specific heat presented is
not characteristic of any obvious ground states, and points to an exotic state
that shows a delicate balance between fluctuations and order.Comment: 18 pages, 4 figure
Numerical and experimental assessment of the modal curvature method for damage detection in plate structures
Use of modal curvatures obtained from modal displacement data for damage detection in isotropic and composite laminated plates is addressed through numerical examples and experimental tests. Numerical simulations are carried out employing COMSOL Multiphysics as finite element solver of the equations governing the Mindlin-Reissner plate model. Damages are introduced as localized non-smooth variations of the bending stiffness of the baseline (healthy) configuration. Experiments are also performed on steel and aluminum plates using scanning laser vibrometry. The obtained results confirm that use of the central difference method to compute modal curvatures greatly amplifies the measurement errors and its application leads to unreliable predictions for damage detection, even after denoising. Therefore, specialized ad hoc numerical techniques must be suitably implemented to enable structural health monitoring via modal curvature changes. In this study, the Savitzky-Golay filter (also referred to as least-square smoothing filter) is considered for the numerical differentiation of noisy data. Numerical and experimental results show that this filter is effective for the reliable computation of modal curvature changes in plate structures due to defects and/or damages
Freezing of Nonlinear Bloch Oscillations in the Generalized Discrete Nonlinear Schrodinger Equation
The dynamics in a nonlinear Schrodinger chain in an homogeneous electric
field is studied. We show that discrete translational invariant
integrability-breaking terms can freeze the Bloch nonlinear oscillations and
introduce new faster frequencies in their dynamics. These phenomena are studied
by direct numerical integration and through an adiabatic approximation. The
adiabatic approximation allows a description in terms of an effective potential
that greatly clarifies the phenomenon.Comment: LaTeX, 7 pages, 6 figures. Improved version to appear in Phys. Rev.
- …