94,543 research outputs found
Laser Mode Bifurcations Induced by -Breaking Exceptional Points
A laser consisting of two independently-pumped resonators can exhibit mode
bifurcations that evolve out of the exceptional points (EPs) of the linear
system at threshold. The EPs are non-Hermitian degeneracies occurring at the
parity/time-reversal () symmetry breaking points of the threshold
system. Above threshold, the EPs become bifurcations of the nonlinear
zero-detuned laser modes, which can be most easily observed by making the gain
saturation intensities in the two resonators substantially different. Small
pump variations can then switch abruptly between different laser behaviors,
e.g. between below-threshold and -broken single-mode operation.Comment: 4 pages, 3 figure
Turbulent mixing of a slightly supercritical Van der Waals fluid at Low-Mach number
Supercritical fluids near the critical point are characterized by liquid-like
densities and gas-like transport properties. These features are purposely
exploited in different contexts ranging from natural products
extraction/fractionation to aerospace propulsion. Large part of studies
concerns this last context, focusing on the dynamics of supercritical fluids at
high Mach number where compressibility and thermodynamics strictly interact.
Despite the widespread use also at low Mach number, the turbulent mixing
properties of slightly supercritical fluids have still not investigated in
detail in this regime. This topic is addressed here by dealing with Direct
Numerical Simulations (DNS) of a coaxial jet of a slightly supercritical Van
der Waals fluid. Since acoustic effects are irrelevant in the Low Mach number
conditions found in many industrial applications, the numerical model is based
on a suitable low-Mach number expansion of the governing equation. According to
experimental observations, the weakly supercritical regime is characterized by
the formation of finger-like structures-- the so-called ligaments --in the
shear layers separating the two streams. The mechanism of ligament formation at
vanishing Mach number is extracted from the simulations and a detailed
statistical characterization is provided. Ligaments always form whenever a high
density contrast occurs, independently of real or perfect gas behaviors. The
difference between real and perfect gas conditions is found in the ligament
small-scale structure. More intense density gradients and thinner interfaces
characterize the near critical fluid in comparison with the smoother behavior
of the perfect gas. A phenomenological interpretation is here provided on the
basis of the real gas thermodynamics properties.Comment: Published on Physics of Fluid
Experimental probing of the anisotropy of the empty p states near the Fermi level in MgB2
We have studied the Boron K-edge in the superconductor MgB2 by electron
energy loss spectroscopy (EELS) and experimentally resolved the empty p states
at the Fermi level that have previously been observed within an energy window
of 0.8eV by soft x-ray absorption spectroscopy. Using angular resolved EELS, we
find that these states at the immediate edge onset have pxy character in
agreement with predictions from first-principle electronic structure
calculations.Comment: 15 pages, 5 figure
Semantic web-based document: editing and browsing in AktiveDoc
This paper presents a tool for supporting sharing and reuse of knowledge in document creation (writing) and use (reading). Semantic Web technologies are used to support the production of ontology based annotations while the document is written. Free text annotations (comments) can be added to integrate the knowledge in the document. In addition the tool uses external services (e.g. a Semantic Web harvester) to propose relevant content to writing
user, enabling easy knowledge reuse. Similar facilities are provided for readers when their task does not coincide with the author’s one. The tool is specifically designed for Knowledge Management in organisations. In this paper we present and discuss how Semantic Web technologies are designed and integrated in the system
Transport in gapped bilayer graphene: the role of potential fluctuations
We employ a dual-gated geometry to control the band gap \Delta in bilayer
graphene and study the temperature dependence of the resistance at the charge
neutrality point, RNP(T), from 220 to 1.5 K. Above 5 K, RNP(T) is dominated by
two thermally activated processes in different temperature regimes and exhibits
exp(T3/T)^{1/3} below 5 K. We develop a simple model to account for the
experimental observations, which highlights the crucial role of localized
states produced by potential fluctuations. The high temperature conduction is
attributed to thermal activation to the mobility edge. The activation energy
approaches \Delta /2 at large band gap. At intermediate and low temperatures,
the dominant conduction mechanisms are nearest neighbor hopping and
variable-range hopping through localized states. Our systematic study provides
a coherent understanding of transport in gapped bilayer graphene.Comment: to appear in Physical Review B: Rapid Com
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