1,597 research outputs found
Random projections and the optimization of an algorithm for phase retrieval
Iterative phase retrieval algorithms typically employ projections onto
constraint subspaces to recover the unknown phases in the Fourier transform of
an image, or, in the case of x-ray crystallography, the electron density of a
molecule. For a general class of algorithms, where the basic iteration is
specified by the difference map, solutions are associated with fixed points of
the map, the attractive character of which determines the effectiveness of the
algorithm. The behavior of the difference map near fixed points is controlled
by the relative orientation of the tangent spaces of the two constraint
subspaces employed by the map. Since the dimensionalities involved are always
large in practical applications, it is appropriate to use random matrix theory
ideas to analyze the average-case convergence at fixed points. Optimal values
of the gamma parameters of the difference map are found which differ somewhat
from the values previously obtained on the assumption of orthogonal tangent
spaces.Comment: 15 page
Stoichiometry and the New Biology: The Future Is Now
There is a call for biological science to move away from the reductionist focus of the past, but there are large-scale integrative efforts already underway; biological stoichiometry provides one such example
Relative importance of Deep Creek Lake to other areas in respect to certain recreational and economic aspects
Presents a review of the recreational values and economic importance of Maryland Fishing waters. (PDF contains 5 pages
Dynamics of immersed molecules in superfluids
The dynamics of a molecule immersed in a superfluid medium are considered.
Results are derived using a classical hydrodynamic approach followed by
canonical quantization. The classical model, a rigid body immersed in
incompressible fluid, permits a thorough analysis; its effective Hamiltonian
generalizes the usual rigid-rotor Hamiltonian. In contrast to the free rigid
rotor, the immersed body is shown to have chaotic dynamics. Quantization of the
classical model leads to new and experimentally verifiable features. It is
shown, for instance, that chiral molecules can behave as "quantum propellers":
the rotational-translational coupling induced by the superfluid leads to a
nonzero linear momentum in the ground state. Hydrogen peroxide is a strong
candidate for experimental detection of this effect. The signature is a
characteristic splitting of rotational absorption lines. The 1_{01} --> 1_{10}
line in hydrogen peroxide, for example, is predicted to split into three lines
separated by as much as 0.01 cm^{-1}, which is about the experimental
linewidth.Comment: 10 pages, 3 figure
Dense packing crystal structures of physical tetrahedra
We present a method for discovering dense packings of general convex hard
particles and apply it to study the dense packing behavior of a one-parameter
family of particles with tetrahedral symmetry representing a deformation of the
ideal mathematical tetrahedron into a less ideal, physical, tetrahedron and all
the way to the sphere. Thus, we also connect the two well studied problems of
sphere packing and tetrahedron packing on a single axis. Our numerical results
uncover a rich optimal-packing behavior, compared to that of other continuous
families of particles previously studied. We present four structures as
candidates for the optimal packing at different values of the parameter,
providing an atlas of crystal structures which might be observed in systems of
nano-particles with tetrahedral symmetry
Soil pH, ecological stoichiometry, and allometric scaling in soil biota
The factors regulating the structure of food webs are a central focus of community and
ecosystem ecology, as trophic interactions among species have important impacts on
nutrient storage and cycling in many ecosystems. For soil invertebrates in grassland
ecosystems in the Netherlands, the site-specific slopes of the faunal biomass to organism body mass relationships reflected basic biochemical and biogeochemical processes associated with soil acidity and soil C:N:P stoichiometry. That is, the higher the phosphorus availability in the soil, the higher, on average, the slope of the faunal biomass size spectrum (i.e., the higher the biomass of large-bodied invertebrates relative to the biomass of small invertebrates). While other factors may also be involved, these results are consistent with the growth rate hypothesis from biological stoichiometry that relates phosphorus demands to ribosomal RNA and protein production. Thus our data represent the first time that ecosystem phosphorus availability has been associated with allometry in soil food webs (supporting information available online). Our results have broad implications, as soil invertebrates of different size have different effects on soil processes
Sub-diffraction light propagation in fibers with anisotropic dielectric cores
We present a detailed study of light propagation in waveguides with
anisotropic metamaterial cores. We demonstrate that in contrast to conventional
optical fibers, our structures support free-space-like propagating modes even
when the waveguide radius is much smaller than the wavelength. We develop
analytical formalism to describe mode structure and propagation in strongly
anisotropic systems and study the effects related to waveguide boundaries and
material composition
Stability of the hard-sphere icosahedral quasilattice
The stability of the hard-sphere icosahedral quasilattice is analyzed using
the differential formulation of the generalized effective liquid approximation.
We find that the icosahedral quasilattice is metastable with respect to the
hard-sphere crystal structures. Our results agree with recent findings by
McCarley and Ashcroft [Phys. Rev. B {\bf 49}, 15600 (1994)] carried out using
the modified weighted density approximation.Comment: 15 pages, 2 figures available from authors upon request, (revtex),
submitted to Phys. Rev.
Scattering-free plasmonic optics with anisotropic metamaterials
We develop an approach to utilize anisotropic metamaterials to solve one of
the fundamental problems of modern plasmonics -- parasitic scattering of
surface waves into free-space modes, opening the road to truly two-dimensional
plasmonic optics. We illustrate the developed formalism on examples of
plasmonic refractor and plasmonic crystal, and discuss limitations of the
developed technique and its possible applications for sensing and imaging
structures, high-performance mode couplers, optical cloaking structures, and
dynamically reconfigurable electro-plasmonic circuits
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