433 research outputs found
Self-focusing and envelope pulse generation in nonlinear magnetic metamaterials
The self-modulation of waves propagating in nonlinear magnetic metamaterials
is investigated. Considering the propagation of a modulated amplitude magnetic
field in such a medium, we show that the self-modulation of the carrier wave
leads to a spontaneous energy localization via the generation of localized
envelope structures (envelope solitons), whose form and properties are
discussed. These results are also supported by numerical calculations.Comment: 4 pages 3 figure
Vertex similarity in networks
We consider methods for quantifying the similarity of vertices in networks.
We propose a measure of similarity based on the concept that two vertices are
similar if their immediate neighbors in the network are themselves similar.
This leads to a self-consistent matrix formulation of similarity that can be
evaluated iteratively using only a knowledge of the adjacency matrix of the
network. We test our similarity measure on computer-generated networks for
which the expected results are known, and on a number of real-world networks
Responses of two scleractinian corals to cobalt pollution and ocean acidification
The effects of ocean acidification alone or in combination with warming on coral metabolism have been extensively investigated, whereas none of these studies consider that most coral reefs near shore are already impacted by other natural anthropogenic inputs such as metal pollution. It is likely that projected ocean acidification levels will aggravate coral reef health. We first investigated how ocean acidification interacts with one near shore locally abundant metal on the physiology of two major reef-building corals: Stylophora pistillata and Acropora muricata. Two pH levels (pH(T) 8.02; pCO(2) 366 mu atm and pH(T) 7.75; pCO(2) 1140 mu atm) and two cobalt concentrations (natural, 0.03 mu g L-1 and polluted, 0.2 mu g L-1) were tested during five weeks in aquaria. We found that, for both species, cobalt input decreased significantly their growth rates by 28% while it stimulated their photosystem II, with higher values of rETR(max) (relative Electron Transport Rate). Elevated pCO(2) levels acted differently on the coral rETR(max) values and did not affect their growth rates. No consistent interaction was found between pCO(2) levels and cobalt concentrations. We also measured in situ the effect of higher cobalt concentrations (1.06 +/- 0.16 mu g L-1) on A. muricata using benthic chamber experiments. At this elevated concentration, cobalt decreased simultaneously coral growth and photosynthetic rates, indicating that the toxic threshold for this pollutant has been reached for both host cells and zooxanthellae. Our results from both aquaria and in situ experiments, suggest that these coral species are not particularly sensitive to high pCO(2) conditions but they are to ecologically relevant cobalt concentrations. Our study reveals that some reefs may be yet subjected to deleterious pollution levels, and even if no interaction between pCO(2) levels and cobalt concentration has been found, it is likely that coral metabolism will be weakened if they are subjected to additional threats such as temperature increase, other heavy metals, and eutrophication
A Precision Angle Sensor using an Optical Lever inside a Sagnac Interferometer
We built an ultra low noise angle sensor by combining a folded optical lever
and a Sagnac interferometer. The instrument has a measured noise floor of 1.3
prad / Hz^(1/2) at 2.4 kHz. We achieve this record angle sensitivity using a
proof-of-concept apparatus with a conservative N=11 bounces in the optical
lever. This technique could be extended to reach sub-picoradian / Hz^(1/2)
sensitivities with an optimized design.Comment: 3 pages, 4 figure
Link Prediction Based on Local Random Walk
The problem of missing link prediction in complex networks has attracted much
attention recently. Two difficulties in link prediction are the sparsity and
huge size of the target networks. Therefore, the design of an efficient and
effective method is of both theoretical interests and practical significance.
In this Letter, we proposed a method based on local random walk, which can give
competitively good prediction or even better prediction than other
random-walk-based methods while has a lower computational complexity.Comment: 6 pages, 2 figure
Effective and Efficient Similarity Index for Link Prediction of Complex Networks
Predictions of missing links of incomplete networks like protein-protein
interaction networks or very likely but not yet existent links in evolutionary
networks like friendship networks in web society can be considered as a
guideline for further experiments or valuable information for web users. In
this paper, we introduce a local path index to estimate the likelihood of the
existence of a link between two nodes. We propose a network model with
controllable density and noise strength in generating links, as well as collect
data of six real networks. Extensive numerical simulations on both modeled
networks and real networks demonstrated the high effectiveness and efficiency
of the local path index compared with two well-known and widely used indices,
the common neighbors and the Katz index. Indeed, the local path index provides
competitively accurate predictions as the Katz index while requires much less
CPU time and memory space, which is therefore a strong candidate for potential
practical applications in data mining of huge-size networks.Comment: 8 pages, 5 figures, 3 table
On the electrodynamics of moving bodies at low velocities
We discuss the seminal article in which Le Bellac and Levy-Leblond have
identified two Galilean limits of electromagnetism, and its modern
implications. We use their results to point out some confusion in the
literature and in the teaching of special relativity and electromagnetism. For
instance, it is not widely recognized that there exist two well defined
non-relativistic limits, so that researchers and teachers are likely to utilize
an incoherent mixture of both. Recent works have shed a new light on the choice
of gauge conditions in classical electromagnetism. We retrieve Le
Bellac-Levy-Leblond's results by examining orders of magnitudes, and then with
a Lorentz-like manifestly covariant approach to Galilean covariance based on a
5-dimensional Minkowski manifold. We emphasize the Riemann-Lorenz approach
based on the vector and scalar potentials as opposed to the Heaviside-Hertz
formulation in terms of electromagnetic fields. We discuss various applications
and experiments, such as in magnetohydrodynamics and electrohydrodynamics,
quantum mechanics, superconductivity, continuous media, etc. Much of the
current technology where waves are not taken into account, is actually based on
Galilean electromagnetism
Dielectrophoresis-Driven Spreading of Immersed Liquid Droplets
In recent years electrowetting-on-dielectric (EWOD) has become an effective tool to control partial wetting. EWOD uses the liquidâsolid interface as part of a capacitive structure that allows capacitive and interfacial energies to adjust by changes in wetting when the liquidâsolid interface is charged due to an applied voltage. An important aspect of EWOD has been its applications in micro fluidics in chemistry and biology and in optical devices and displays in physics and engineering. Many of these rely on the use of a liquid droplet immersed in a second liquid due to the need either for neutral buoyancy to overcome gravity and shield against impact shocks or to encapsulate the droplet for other reasons, such as in microfluidic-based DNA analyses. Recently, it has been shown that nonwetting oleophobic surfaces can be forcibly wetted by nonconducting oils using nonuniform electric fields and an interface-localized form of liquid dielectrophoresis (dielectrowetting). Here we show that this effect can be used to create films of oil immersed in a second immiscible fluid of lower permittivity. We predict that the square of the thickness of the film should obey a simple law dependent on the square of the applied voltage and with strength dependent on the ratio of difference in permittivity to the liquid-fluid interfacial tension, ÎΔ/ÎłLF. This relationship is experimentally confirmed for 11 liquidâair and liquidâliquid combinations with ÎΔ/ÎłLF having a span of more than two orders of magnitude. We therefore provide fundamental understanding of dielectrowetting for liquid-in-liquid systems and also open up a new method to determine liquidâliquid interfacial tensions
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