24,125 research outputs found
Luminosity segregation versus fractal scaling in the galaxy distribution
In this letter I present results from a correlation analysis of three galaxy
redshift catalogs: the SSRS2, the CfA2 and the PSCz. I will focus on the
observation that the amplitude of the two--point correlation function rises if
the depth of the sample is increased. There are two competing explanations for
this observation, one in terms of a fractal scaling, the other based on
luminosity segregation. I will show that there is strong evidence that the
observed growth is due to a luminosity dependent clustering of the galaxies.Comment: 7 pages, EPL in pres
Formation of corner waves in the wake of a partially submerged bluff body
We study theoretically and numerically the downstream flow near the corner of a bluff body partially submerged at a deadrise depth Δh into a uniform stream of velocity U, in the presence of gravity, g. When the Froude number, Fr=U/√gΔh, is large, a three-dimensional steady plunging wave, which is referred to as a corner wave, forms near the corner, developing downstream in a similar way to a two-dimensional plunging wave evolving in time. We have performed an asymptotic analysis of the flow near this corner to describe the wave's initial evolution and to clarify the physical mechanism that leads to its formation. Using the two-dimensions-plus-time approximation, the problem reduces to one similar to dam-break flow with a wet bed in front of the dam. The analysis shows that, at leading order, the problem admits a self-similar formulation when the size of the wave is small compared with the height difference Δh. The essential feature of the self-similar solution is the formation of a mushroom-shaped jet from which two smaller lateral jets stem. However, numerical simulations show that this self-similar solution is questionable from the physical point of view, as the two lateral jets plunge onto the free surface, leading to a self-intersecting flow. The physical mechanism leading to the formation of the mushroom-shaped structure is discussed
Physical qubits from charged particles: IR divergences in quantum information
We consider soft photons effects (IR structure of QED) on the construction of
physical qubits. Soft-photons appear when we build charged qubits from the
asymptotic states of QED. This construction is necessary in order to include
the effect of soft photons on entanglement measures. The nonexistence of free
charged particles (due to the long range of QED interactions) lead us to
question the sense of the very concept of free charged qubit. In this letter,
using the "dressing" formalism, we build physical charged qubits from dressed
fields which have the correct asymptotic behavior, are gauge invariant, their
propagators have a particle pole structure and are free from infrared
divergences. Finally, we discuss the impact of the soft corrections on the
entanglement measures.Comment: 4 pages, 2 figures, RevTeX. Version 2: Some references update
Nongalvanic thermometry for ultracold two-dimensional electron domains
Measuring the temperature of a two-dimensional electron gas at temperatures
of a few mK is a challenging issue, which standard thermometry schemes may fail
to tackle. We propose and analyze a nongalvanic thermometer, based on a quantum
point contact and quantum dot, which delivers virtually no power to the
electron system to be measured.Comment: 5 pages, 3 figure
Ratchet potential for fluxons in Josephson-Junction arrays
We propose a simple configuration of a one-dimensional parallel array of
Josephson junctions in which the pinning potential for trapped fluxons lacks
inversion symmetry (ratchet potential). This sytem can be modelised by a set of
non-linear pendula with alternating lengths and harmonic couplings. We show, by
molecular dynamics simulations, that fluxons behave as single particles in
which the predictions for overdamped thermal ratchet can be easily verified.Comment: 7 pages, 8 figure
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