658 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
Greenberger-Horne-Zeilinger state protocols for fully connected qubit networks
We generalize the recently proposed Greenberger-Horne-Zeilinger (GHZ)
tripartite protocol [A. Galiautdinov, J. M. Martinis, Phys. Rev. A 78,
010305(R) (2008)] to fully connected networks of weakly coupled qubits
interacting by way of anisotropic Heisenberg exchange g(XX+YY)+g1*ZZ. Our model
adopted here differs from the more familiar Ising-Heisenberg chain in that here
every qubit interacts with every other qubit in the circuit. The assumption of
identical couplings on all qubit pairs allows an elegant proof of the protocol
for arbitrary N. In order to further make contact with experiment, we study
fidelity degradation due to coupling imperfections by numerically simulating
the N=3 and N=4 cases. Our simulations indicate that the best fidelity at
unequal couplings is achieved when (a) the system is initially prepared in the
uniform superposition state (similarly to how it is done in the ideal case),
and (b) the entangling time and the final rotations on each of the qubits are
appropriately adjusted.Comment: 11 pages, 1 figur
Numerical simulation of ionospheric depletions resulting from rocket launches using a general circulation model
Rocket exhaust plumes have been observed to cause large-scale depletions of
ionospheric plasmas ("ionospheric holes"). In the F-region, charge exchange
reactions occur between O^+ ions and exhaust species such as HO, H, and
CO to form ions which then undergo rapid dissociative recombination. The
Global Ionosphere-Thermosphere Model (GITM) was extended to include these
chemical reactions and appropriate source terms to represent rocket exhaust
plumes. The resulting model was applied to ionospheric depletions resulting
from the launches of Jason-3 and FORMOSAT-5 on SpaceX Falcon 9 rockets from
Vandenberg Air Force Base. Outputs from the model were compared with GNSS,
ionosonde, and satellite Langmuir probe measurements. Simulation indicated that
the FORMOSAT-5 launch resulted in a far larger and longer-lived ionospheric
depletion than the Jason-3 launch, consistent with observations.Comment: 33 pages, 13 figures, 3 table
Light-regulated plant growth and development.
Plants are sessile and photo-autotrophic; their entire life cycle is thus strongly influenced by the ever-changing light environment. In order to sense and respond to those fluctuating conditions higher plants possess several families of photoreceptors that can monitor light from UV-B to the near infrared (far-red). The molecular nature of UV-B sensors remains unknown, red (R) and far-red (FR) light is sensed by the phytochromes (phyA-phyE in Arabidopsis) while three classes of UV-A/blue photoreceptors have been identified: cryptochromes, phototropins, and members of the Zeitlupe family (cry1, cry2, phot1, phot2, ZTL, FKF1, and LKP2 in Arabidopsis). Functional specialization within photoreceptor families gave rise to members optimized for a wide range of light intensities. Genetic and photobiological studies performed in Arabidopsis have shown that these light sensors mediate numerous adaptive responses (e.g., phototropism and shade avoidance) and developmental transitions (e.g., germination and flowering). Some physiological responses are specifically triggered by a single photoreceptor but in many cases multiple light sensors ensure a coordinated response. Recent studies also provide examples of crosstalk between the responses of Arabidopsis to different external factors, in particular among light, temperature, and pathogens. Although the different photoreceptors are unrelated in structure, in many cases they trigger similar signaling mechanisms including light-regulated protein-protein interactions or light-regulated stability of several transcription factors. The breath and complexity of this topic forced us to concentrate on specific aspects of photomorphogenesis and we point the readers to recent reviews for some aspects of light-mediated signaling (e.g., transition to flowering)
Direct generation of charge carriers in c-Si solar cells due to embedded nanoparticles
It is known that silicon is an indirect band gap material, reducing its
efficiency in photovoltaic applications. Using surface plasmons in metallic
nanoparticles embedded in a solar cell has recently been proposed as a way to
increase the efficiency of thin film silicon solar cells. The dipole mode that
dominates the plasmons in small particles produces an electric field having
Fourier components with all wave numbers. In this work, we show that such a
field creates electron-hole-pairs without phonon assistance, and discuss the
importance of this effect compared to radiation from the particle and losses
due to heating.Comment: 1 figur
Inhibition of the shade avoidance response by formation of non-DNA binding bHLH heterodimers.
In shade-intolerant plants such as Arabidopsis, a reduction in the red/far-red (R/FR) ratio, indicative of competition from other plants, triggers a suite of responses known as the shade avoidance syndrome (SAS). The phytochrome photoreceptors measure the R/FR ratio and control the SAS. The phytochrome-interacting factors 4 and 5 (PIF4 and PIF5) are stabilized in the shade and are required for a full SAS, whereas the related bHLH factor HFR1 (long hypocotyl in FR light) is transcriptionally induced by shade and inhibits this response. Here we show that HFR1 interacts with PIF4 and PIF5 and limits their capacity to induce the expression of shade marker genes and to promote elongation growth. HFR1 directly inhibits these PIFs by forming non-DNA-binding heterodimers with PIF4 and PIF5. Our data indicate that PIF4 and PIF5 promote SAS by directly binding to G-boxes present in the promoter of shade marker genes, but their action is limited later in the shade when HFR1 accumulates and forms non-DNA-binding heterodimers. This negative feedback loop is important to limit the response of plants to shade
Derivation of the Lorentz Force Law, the Magnetic Field Concept and the Faraday-Lenz Law using an Invariant Formulation of the Lorentz Transformation
It is demonstrated how the right hand sides of the Lorentz Transformation
equations may be written, in a Lorentz invariant manner, as 4--vector scalar
products. This implies the existence of invariant length intervals analogous to
invariant proper time intervals. This formalism, making essential use of the
4-vector electromagnetic potential concept, provides a short derivation of the
Lorentz force law of classical electrodynamics, the conventional definition of
the magnetic field, in terms of spatial derivatives of the 4--vector potential
and the Faraday-Lenz Law. An important distinction between the physical
meanings of the space-time and energy-momentum 4--vectors is pointed out.Comment: 15 pages, no tables 1 figure. Revised and extended version of
physics/0307133 Some typos removed and minor text improvements in this
versio
Electromagnetic force density in dissipative isotropic media
We derive an expression for the macroscopic force density that a narrow-band
electromagnetic field imposes on a dissipative isotropic medium. The result is
obtained by averaging the microscopic form for Lorentz force density. The
derived expression allows us to calculate realistic electromagnetic forces in a
wide range of materials that are described by complex-valued electric
permittivity and magnetic permeability. The three-dimensional energy-momentum
tensor in our expression reduces for lossless media to the so-called Helmholtz
tensor that has not been contradicted in any experiment so far. The momentum
density of the field does not coincide with any well-known expression, but for
non-magnetic materials it matches the Abraham expression
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
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