1,436 research outputs found
Anderson Localization of Polar Eigenmodes in Random Planar Composites
Anderson localization of classical waves in disordered media is a fundamental
physical phenomenon that has attracted attention in the past three decades.
More recently, localization of polar excitations in nanostructured
metal-dielectric films (also known as random planar composite) has been subject
of intense studies. Potential applications of planar composites include local
near-field microscopy and spectroscopy. A number of previous studies have
relied on the quasistatic approximation and a direct analogy with localization
of electrons in disordered solids. Here I consider the localization problem
without the quasistatic approximation. I show that localization of polar
excitations is characterized by algebraic rather than by exponential spatial
confinement. This result is also valid in two and three dimensions. I also show
that the previously used localization criterion based on the gyration radius of
eigenmodes is inconsistent with both exponential and algebraic localization. An
alternative criterion based on the dipole participation number is proposed.
Numerical demonstration of a localization-delocalization transition is given.
Finally, it is shown that, contrary to the previous belief, localized modes can
be effectively coupled to running waves.Comment: 22 pages, 7 figures. Paper was revised and a more precise definition
of the participation number given, data for figures recalculated accordingly.
Accepted to J. Phys.: Cond. Mat
Coherently tunable third-order nonlinearity in a nanojunction
A possibility of tuning the phase of the third-order Kerr-type nonlinear
susceptibility in a system consisting of two interacting metal nanospheres and
a nonlinearly polarizable molecule is investigated theoretically and
numerically. It is shown that by varying the relative inter-sphere separation,
it is possible to tune the phase of the effective nonlinear susceptibility
\chi^{(3)}(\omega;\omega,\omega,-\omega)2\pi$.Comment: 10 pages 5 figure
Rethinking Criminal Law and Family Status
In our recent book, Privilege or Punish: Criminal Justice and the Challenge of Family Ties (OUP 2009), we examined and critiqued a number of ways in which the criminal justice system uses family status to distribute benefits or burdens to defendants. In their review essays, Professors Alafair Burke, Alice Ristroph & Melissa Murray identify a series of concerns with the framework we offer policymakers to analyze these family ties benefits or burdens. We think it worthwhile not only to clarify where those challenges rest on misunderstandings or confusions about the central features of our views, but also to show the deficiencies of the proposed alternatives. While we appreciate and admire the efforts of our critics to advance this important conversation, we hope this Essay will illuminate why the normative framework of Privilege or Punish remains a more helpful structure to policymakers assessing how family status should intersect with the criminal law within a liberal democracy such as our own
Reciprocity relation for the vector radiative transport equation and its application to diffuse optical tomography with polarized light
We derive a reciprocity relation for vector radiative transport equation
(vRTE) that describes propagation of polarized light in multiple-scattering
media. We then show how this result, together with translational invariance of
a plane-parallel sample, can be used to compute efficiently the sensitivity
kernel of diffuse optical tomography (DOT) by Monte Carlo simulations.
Numerical examples of polarization-selective sensitivity kernels thus computed
are given.Comment: 5 pages, 3 figure
Comment on "Optical Response of Strongly Coupled Nanopraticles in Dimer Arrays" (Phys. Rev. B 71(4), 045404, 2005)
I have re-calculated the extinction spectra of aggregates of two silver
nanospheres shown in Figs.~2 and 3 of Ref.~8. I have used the approximate
method of images according to Ref.~8 and an exact numerical technique. I have
found that the three sets of data (those I have obtained by the method of
images, the numerical results, and the results published in Ref.~8) do not
coincide. In this Comment, I discuss the reasons for these discrepancies and
the general applicability of the method of images to the quasi-static
electromagnetic problem of two interacting nanospheres.Comment: 4 pages, 4 figures, submitted to Phys. Rev.
Multiple Projection Optical Diffusion Tomography with Plane Wave Illumination
We describe a new data collection scheme for optical diffusion tomography in
which plane wave illumination is combined with multiple projections in the slab
imaging geometry. Multiple projection measurements are performed by rotating
the slab around the sample. The advantage of the proposed method is that the
measured data can be much more easily fitted into the dynamic range of most
commonly used detectors. At the same time, multiple projections improve image
quality by mutually interchanging the depth and transverse directions, and the
scanned (detection) and integrated (illumination) surfaces. Inversion methods
are derived for image reconstructions with extremely large data sets. Numerical
simulations are performed for fixed and rotated slabs
Comments on the nonpharmaceutical interventions in New York City and Chicago during the 1918 flu pandemic
This commentary was originally published in CIDRAP News and it is here reported almost verbatim to allow divulgation through open access. The Editorial summarizes John Barry's concerns about the value of accurate historical reporting and its implications in public policy determination. This short abstract was written by the Editor-in-Chief of the Journal of Translational Medicine to introduce the Editorial
Nonpharmaceutical Interventions Implemented by US Cities During the 1918–1919 Influenza Pandemic
Local anisotropy and giant enhancement of local electromagnetic fields in fractal aggregates of metal nanoparticles
We have shown within the quasistatic approximation that the giant
fluctuations of local electromagnetic field in random fractal aggregates of
silver nanospheres are strongly correlated with a local anisotropy factor S
which is defined in this paper. The latter is a purely geometrical parameter
which characterizes the deviation of local environment of a given nanosphere in
an aggregate from spherical symmetry. Therefore, it is possible to predict the
sites with anomalously large local fields in an aggregate without explicitly
solving the electromagnetic problem. We have also demonstrated that the average
(over nanospheres) value of S does not depend noticeably on the fractal
dimension D, except when D approaches the trivial limit D=3. In this case, as
one can expect, the average local environment becomes spherically symmetrical
and S approaches zero. This corresponds to the well-known fact that in trivial
aggregates fluctuations of local electromagnetic fields are much weaker than in
fractal aggregates. Thus, we find that, within the quasistatics, the
large-scale geometry does not have a significant impact on local
electromagnetic responses in nanoaggregates in a wide range of fractal
dimensions. However, this prediction is expected to be not correct in
aggregates which are sufficiently large for the intermediate- and
radiation-zone interaction of individual nanospheres to become important.Comment: 9 pages 9 figures. No revisions from previous version; only figure
layout is change
Inversion formulas for the broken-ray Radon transform
We consider the inverse problem of the broken ray transform (sometimes also
referred to as the V-line transform). Explicit image reconstruction formulas
are derived and tested numerically. The obtained formulas are generalizations
of the filtered backprojection formula of the conventional Radon transform. The
advantages of the broken ray transform include the possibility to reconstruct
the absorption and the scattering coefficients of the medium simultaneously and
the possibility to utilize scattered radiation which, in the case of the
conventional X-ray tomography, is typically discarded.Comment: To be submitted to Inverse Problem
- …