Making Metals Transparent
Making metallic materials transparent, which could lead to various
fascinating applications, has long been imagined. However, transparent
metals previously only existed in science fiction, featuring in the
movie Star Trek IV. Naturally all bulk metals are not transparent to
electromagnetic waves from ultraviolet radiation to microwaves. Here we
theoretical demonstrate a very simple way to make structured metals
transparent (at least for long wavelengths). By perforating metal plates
with narrow slit arrays, we show that the plates may become transparent
for extremely broad bandwidths under oblique-incidence geometry. The
underlying principle is that the incident wave is tunneled by moving
electrons on the slit walls as spoof surface plasmons. This mechanism
gives clear guidelines to the development of many novel plasmonic
devices, including white-beam polarizers, transparent metal windows,
anti-reflection surfaces, broadband metamaterials, etc.
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AW10667
Atoms guiding light guiding atoms: the dance of atoms and light.
Consider a bunch of cold atoms, a Bose-Einstein condensate in fact. In spite of the atoms being very close to the absolute zero, quantum mechanics (or nature?) gives them the tendency to spread out because of their zero-point energy. Besides, atoms being atoms, they interact and we are considering atoms which repel each other, albeit weakly (this adds to their tendency to spread out). Now imagine to shine laser light on these atoms. You are showering them with electromagnetic radiation and, since atoms are electromagnetic creatures, they will respond to the radiation. It seems possible that the essence of this response, the atom reaction cleaned of all possible incoherent effects, is for the atoms to modify their natural tendency to spread out and even transform it into a localizing phenomenon following the laser intensity. At the same time light, an electromagnetic creature itself, responds to electromagnetic interactions with the BEC and the natural tendency of the laser light to broaden can change into a solitary-like behavior. A dance starts, where atoms guide light which guide atoms. For any application we may have in mind, we must be able to stir and guide atoms. Maybe nature is suggesting a way to achieve this.
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LU12174BR
Riddle of supersolidity
Supersolidity, flow of solid matter through itself without resistance,
has been observed in solid helium in laboratories throughout the world
since its discovery in 2004. To this day, the explanation of this
startling phenomenon remains elusive. One possibility is presence of
defects in the crystalline lattice of the solid, especially of
vacancies, even at very low temperatures. Vacancy is a small void in
the crystalline structure, essentially a missing atom. We have calculated quantum-mechanically the properties of
vacancies in solid helium under constant pressure conditions. They
found that both energy of creating such defects and the size of the
resulting deformations closely mimic the supersolid signal?s
experimental dependence on pressure. While these findings do not
explain the supersolidity by itself, they provide some much needed
clues and directions for further search.
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ET10663
Material Scaling Laws from Static Micro-tomographic Images
Micro-tomography reveals 3-D microstructure of materials at submicron resolution. In rare cases a series of microstructural images are available from experiments from which material scaling laws can be derived directly. Most often, such experiments revealing the critical percolation threshold are rarely available. The experimentalist is confronted with static micro-tomographic images of the material. This paper formulates and verifies a new method for obtaining percolation threshold for any specific structures from such static images. The method consists of generating derivative models by deflating and inflating operations of mathematical morphology from such micro- tomography results. The method uncovers the critical exponent of correlation length and fractal dimension for all materials with random microstructure. This study greatly improves the potential applications of micro-tomography in material science and can be used for upscaling material properties from micro- to mesoscale.
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ET10568
Increasing the resilience of the US passenger airlines
Ensuring the smooth operation of airline networks is crucial to the
global economy. While past studies have focused on the composite view
of all airlines integrated together, the authors of the current study
focus on the individual carriers and how each carrier might
individually increase its resilience. Using the concept of k-cores (a
subgraph constructed from the network by iteratively pruning all
vertices with degree less than k), they find that some airline
networks have a special structure significantly different from the
rest. Networks with dense interconnectivity, as quantified by large
k-cores for high values of k, are extremely resilient to both targeted
removal of airports (nodes) and random removal of flight paths
(edges). The authors also find that such networks stay connected and
incur minimal increase in an heuristic travel time despite removal of
a majority of nodes or edges. This paper also introduces network
rewiring schemes that boost resilience to different levels of
perturbation while preserving total number of flight and gate
requirements (which, in a general network, corresponds to node
strength). Recent studies have focused on the asymptotic optimality
of hub-and-spoke spatial networks under normal operating conditions,
while the results from this paper indicate that point-to-point
architectures can be much more resilient to perturbations, especially
in networks with a few hundred nodes.
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LT12482ER
Understanding transport in complex networks: traffic and connectivity
govern dispersion
The study of networks as complex systems has revolutionized many
disciplines in physics and the social and natural sciences. Recently,
the focus of network science has shifted from the analysis of the
network topology to the study of the dynamics of processes that take
place on them, such as information flow, disease spreading, and
adoption of ideas. In this paper, we show that the rate at which
agents spread on a network under a purely random walk is independent
of the network topology. In contrast, spreading under drift, or bias,
exhibits an entirely different behavior. When the migration of agents
reflects traffic in the network—driven by flow, sources and sinks, or
a set of incentives—spreading is super-diffusive and highly dependent
on network connectivity. This finding has important implications for
understanding the vulnerability and resilience of complex networks
against carriers that are transported through the network, as well as
for designing optimal mitigation strategies against outbreaks.
