43,185 research outputs found
Robust ecological pattern formation induced by demographic noise
We demonstrate that demographic noise can induce persistent spatial pattern
formation and temporal oscillations in the Levin-Segel predator-prey model for
plankton-herbivore population dynamics. Although the model exhibits a Turing
instability in mean field theory, demographic noise greatly enlarges the region
of parameter space where pattern formation occurs. To distinguish between
patterns generated by fluctuations and those present at the mean field level in
real ecosystems, we calculate the power spectrum in the noise-driven case and
predict the presence of fat tails not present in the mean field case. These
results may account for the prevalence of large-scale ecological patterns,
beyond that expected from traditional non-stochastic approaches.Comment: Revised version. Supporting simulation at:
http://guava.physics.uiuc.edu/~tom/Netlogo
Focusing Light through Random Photonic Media by Binary Amplitude Modulation
We study the focusing of light through random photonic materials using
wavefront shaping. We explore a novel approach namely binary amplitude
modulation. To this end, the light incident to a random photonic medium is
spatially divided into a number of segments. We identify the segments that give
rise to fields that are out of phase with the total field at the intended focus
and assign these a zero amplitude, whereas the remaining segments maintain
their original amplitude. Using 812 independently controlled segments of light,
we find the intensity at the target to be 75 +/- 6 times enhanced over the
average intensity behind the sample. We experimentally demonstrate focusing of
light through random photonic media using both an amplitude only mode liquid
crystal spatial light modulator and a MEMS-based spatial light modulator. Our
use of Micro Electro-Mechanical System (MEMS)-based digital micromirror devices
for the control of the incident light field opens an avenue to high speed
implementations of wavefront shaping
Approaches to Diversity Education: A Critical Assessment
The idea that differences in race, gender, religion, sexuality, age - or other categories deemed unworthy of group inclusion shouldn’t matter when it comes to people’s access to all that a society has to offer is central to the teaching of diversity. Diversity courses can be powerful vehicles, not only for teaching students about social change and reclaiming the principles of past and present civil rights leaders, but also for refuting the notion that we already live in a largely egalitarian society.
This paper examines what a small sample of diversity texts employ with respect to key concepts and definitions. It also makes recommendations for changes and tools to help move the discussion from diversity and tolerance to inclusion and social justice. Lastly, it argues that there is need for specific training for faculty who teach about diversity in order for them to be prepared for some of the critical questions they will be asked by their students
Partial nonlinear reciprocity breaking through ultrafast dynamics in a random photonic medium
We demonstrate that ultrafast nonlinear dynamics gives rise to reciprocity
breaking in a random photonic medium. Reciprocity breaking is observed via the
suppression of coherent backscattering, a manifestation of weak localization of
light. The effect is observed in a pump-probe configuration where the pump
induces an ultrafast step-change of the refractive index during the dwell time
of the probe light in the material. The dynamical suppression of coherent
backscattering is reproduced well by a multiple scattering Monte Carlo
simulation. Ultrafast reciprocity breaking provides a distinct mechanism in
nonlinear optical media which opens up avenues for the active manipulation of
mesoscopic transport, random lasers, and photon localization.Comment: 5 pages, 4 figure
Convergence and multiplicities for the Lempert function
Given a domain , the Lempert function is a
functional on the space Hol (\D,\Omega) of analytic disks with values in
, depending on a set of poles in . We generalize its definition
to the case where poles have multiplicities given by local indicators (in the
sense of Rashkovskii's work) to obtain a function which still dominates the
corresponding Green function, behaves relatively well under limits, and is
monotonic with respect to the indicators. In particular, this is an improvement
over the previous generalization used by the same authors to find an example of
a set of poles in the bidisk so that the (usual) Green and Lempert functions
differ.Comment: 24 pages; many typos corrected thanks to the referee of Arkiv for
Matemati
Mutations in human dynamin block an intermediate stage in coated vesicle formation
The role of human dynamin in receptor-mediated endocytosis was investigated by transient expression of GTP-binding domain mutants in mammalian cells. Using assays which detect intermediates in coated vesicle formation, the dynamin mutants were found to block endocytosis at a stage after the initiation of coat assembly and preceding the sequestration of ligands into deeply invaginated coated pits. Membrane transport from the ER to the Golgi complex was unaffected indicating that dynamin mutants specifically block early events in endocytosis. These results demonstrate that mutations in the GTP-binding domain of dynamin block Tfn-endocytosis in mammalian cells and suggest that a functional dynamin GTPase is required for receptor-mediated endocytosis via clathrin-coated pits
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