4,536 research outputs found
Investigation of empennage buffeting
Theoretical methods of predicting aircraft buffeting are reviewed. For the buffeting due to leading edge vortex breakdown, a method is developed to convert test data of mean square values of fluctuating normal force to buffeting vortex strength through an unsteady lifting-surface theory and unsteady suction analogy. The resulting buffeting vortex from the leading edge extension of an F-18 configuration is used to generate a fluctuating flow field which produces unsteady pressure distribution on the vertical tails. The root mean square values of root bending moment on the vertical tails are calculated for a rigid configuration
Local orbital-angular-momentum dependent surface states with topological protection
Chiral surface states along the zigzag edge of a valley photonic crystal in
the honeycomb lattice are demonstrated. By decomposing the local fields into
orbital angular momentum (OAM) modes, we find that the chiral surface states
present OAM-dependent unidirectional propagation characteristics. Particularly,
the propagation directivities of the surface states are quantified by the local
OAM decomposition and are found to depend on the chiralities of both the source
and surface states. These findings allow for the engineering control of the
unidirectional propagation of electromagnetic energy without requiring an
ancillary cladding layer. Furthermore, we examine the propagation of the chiral
surface states against sharp bends. It turns out that although only certain
states successfully pass through the bend, the unidirectional propagation is
well maintained due to the topology of the structure.Comment: 9 pages, 6 figure
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The glucocorticoid-Angptl4-ceramide axis induces insulin resistance through PP2A and PKCζ.
Chronic glucocorticoid exposure is associated with the development of insulin resistance. We showed that glucocorticoid-induced insulin resistance was attenuated upon ablation of Angptl4, a glucocorticoid target gene encoding the secreted protein angiopoietin-like 4, which mediates glucocorticoid-induced lipolysis in white adipose tissue. Through metabolomic profiling, we revealed that glucocorticoid treatment increased hepatic ceramide concentrations by inducing enzymes in the ceramide synthetic pathway in an Angptl4-dependent manner. Angptl4 was also required for glucocorticoids to stimulate the activities of the downstream effectors of ceramide, protein phosphatase 2A (PP2A) and protein kinase Cζ (PKCζ). We further showed that knockdown of PP2A or inhibition of PKCζ or ceramide synthesis prevented glucocorticoid-induced glucose intolerance in wild-type mice. Moreover, the inhibition of PKCζ or ceramide synthesis did not further improve glucose tolerance in Angptl4-/- mice, suggesting that these molecules were major downstream effectors of Angptl4. Overall, our study demonstrates the key role of Angptl4 in glucocorticoid-augmented hepatic ceramide production that induces whole-body insulin resistance
Second-harmonic generation via double topological valley-Hall kink modes in all-dielectric photonic crystals
Nonlinear topological photonics, which explores topics common to the fields
of topological phases and nonlinear optics, is expected to open up a new
paradigm in topological photonics. Here, we demonstrate second-harmonic
generation via nonlinear interaction of double topological valley-Hall kink
modes in all-dielectric photonic crystals. We first show that two topological
frequency bandgaps can be created around a pair of frequencies, and
, by gapping out the corresponding Dirac points in two-dimensional
honeycomb photonic crystals. Valley-Hall kink modes along a kink-type domain
wall interface between two photonic crystals placed together in a
mirror-symmetric manner are generated within the two frequency bandgaps.
Importantly, through full-wave simulations and mode dispersion analysis, we
demonstrate that tunable, bi-directional phase-matched second-harmonic
generation via nonlinear interaction of the valley-Hall kink modes within the
two frequency bandgaps could be achieved. Our work opens up new avenues towards
topologically protected nonlinear frequency mixing in optics using
all-dielectric materials.Comment: 5 pages, 4 figure
A brief review of topological photonics in one, two, and three dimensions
Topological photonics has attracted increasing attention in recent years due
to the unique opportunities it provides to manipulate light in a robust way
immune to disorder and defects. Up to now, diverse photonic platforms, rich
physical mechanisms and fruitful device applications have been proposed for
topological photonics, including one-way waveguide, topological lasing,
topological nanocavity, Dirac and Weyl points, Fermi arcs, nodal lines, etc. In
this review, we provide an introduction to the field of topological photonics
through the lens of topological invariants and bulk-boundary correspondence in
one, two, and three dimensions, which may not only offer a unified
understanding about the underlying robustness of diverse and distinct
topological phenomena of light, but could also inspire further developments by
introducing new topological invariants and unconventional bulk-boundary
correspondence to the research of topological photonics.Comment: 29 pages, 12 figures, 341 reference
Towards granular hydrodynamics in two-dimensions
We study steady-state properties of inelastic gases in two-dimensions in the
presence of an energy source. We generalize previous hydrodynamic treatments to
situations where high and low density regions coexist. The theoretical
predictions compare well with numerical simulations in the nearly elastic
limit. It is also seen that the system can achieve a nonequilibrium
steady-state with asymmetric velocity distributions, and we discuss the
conditions under which such situations occur.Comment: 8 pages, 9 figures, revtex, references added, also available from
http://arnold.uchicago.edu/?ebn
Prospects for the Search for a Standard Model Higgs Boson in ATLAS using Vector Boson Fusion
The potential for the discovery of a Standard Model Higgs boson in the mass
range m_H < 2 m_Z in the vector boson fusion mode has been studied for the
ATLAS experiment at the LHC. The characteristic signatures of additional jets
in the forward regions of the detector and of low jet activity in the central
region allow for an efficient background rejection. Analyses for the H -> WW
and H -> tau tau decay modes have been performed using a realistic simulation
of the expected detector performance. The results obtained demonstrate the
large discovery potential in the H -> WW decay channel and the sensitivity to
Higgs boson decays into tau-pairs in the low-mass region around 120 GeV.Comment: 20 pages, 13 ps figures, uses EPJ style fil
Statistical Laws Governing Fluctuations in Word Use from Word Birth to Word Death
We analyze the dynamic properties of 10^7 words recorded in English, Spanish
and Hebrew over the period 1800--2008 in order to gain insight into the
coevolution of language and culture. We report language independent patterns
useful as benchmarks for theoretical models of language evolution. A
significantly decreasing (increasing) trend in the birth (death) rate of words
indicates a recent shift in the selection laws governing word use. For new
words, we observe a peak in the growth-rate fluctuations around 40 years after
introduction, consistent with the typical entry time into standard dictionaries
and the human generational timescale. Pronounced changes in the dynamics of
language during periods of war shows that word correlations, occurring across
time and between words, are largely influenced by coevolutionary social,
technological, and political factors. We quantify cultural memory by analyzing
the long-term correlations in the use of individual words using detrended
fluctuation analysis.Comment: Version 1: 31 pages, 17 figures, 3 tables. Version 2 is streamlined,
eliminates substantial material and incorporates referee comments: 19 pages,
14 figures, 3 table
First-principle calculation of Chern number in gyrotropic photonic crystals
As an important figure of merit for characterizing the quantized collective
behaviors of the wavefunction, Chern number is the topological invariant of
quantum Hall insulators. Chern number also identifies the topological
properties of the photonic topological insulators (PTIs), thus it is of crucial
importance in PTI design. In this paper, we develop a first principle
computatioal method for the Chern number of 2D gyrotropic photonic crystals
(PCs), starting from the Maxwell's equations. Firstly, we solve the Hermitian
generalized eigenvalue equation reformulated from the Maxwell's equations by
using the full-wave finite-difference frequency-domain (FDFD) method. Then the
Chern number is obtained by calculating the integral of Berry curvature over
the first Brillouin zone. Numerical examples of both transverse-electric (TE)
and transverse-magnetic (TM) modes are demonstrated, where convergent Chern
numbers can be obtained using rather coarse grids, thus validating the
efficiency and accuracy of the proposed method.Comment: 13 pages, 6 figure
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