10,020 research outputs found
Spatial dependence of gain nonlinearities in InGaAs semiconductor optical amplifier
Counter-propagating sub-picosecond pulses are used to monitor gain saturation along the waveguide of an InGaAs superlattice semiconductor optical amplifier at 1550 nm wavelength. The functional form of the spatial dependence of gain saturation is found to depend on pulse energy. These observations are interpreted by combining the optical nonlinearities associated with interband carrier dynamics and carrier heating together and their respective time constants. We show that the results are consistent with the predictions of a propagation model. Implications for all-optical switching, particularly in the limit of full saturation across the whole amplifier, are discussed. (c) 2005 American Institute of Physics.</p
The X-ray luminosity function of galaxies in the Coma cluster
The XMM-Newton survey of the Coma cluster of galaxies covers an area of 1.86
square degrees with a mosaic of 16 pointings and has a total useful integration
time of 400 ksec. Detected X-ray sources with extent less than 10" were
correlated with cataloged galaxies in the Coma cluster region. The redshift
information, which is abundant in this region of the sky, allowed us to
separate cluster members from background and foreground galaxies. For the
background sources, we recover a typical LogN-LogS in the flux range 1.e-15 -
1.e-13 ergs/s/cm^2 in the 0.5-2.0 keV band. The X-ray emission from the cluster
galaxies exhibits X-ray colors typical of thermal emission. The luminosities of
Coma galaxies lie in the 1.e39-1.e41 ergs/s interval in the 0.5-2.0 keV band.
The luminosity function of Coma galaxies reveals that their X-ray activity is
suppressed with respect to the field by a factor of 5.6, indicating a lower
level of X-ray emission for a given stellar mass.Comment: 16 pages, 2004 A&A in pres
Multiple merging in the Abell cluster 1367
We present a dynamical analysis of the central ~1.3 square degrees of the
cluster of galaxies Abell 1367, based on 273 redshift measurements (of which
119 are news). From the analysis of the 146 confirmed cluster members we derive
a significantly non-Gaussian velocity distribution, with a mean location C_{BI}
= 6484+/-81 km/s and a scale S_{BI} = 891+/-58 km/s. The cluster appears
elongated from the North-West to the South-East with two main density peaks
associated with two substructures. The North-West subcluster is probably in the
early phase of merging into the South-East substructure (~ 0.2 Gyr before core
crossing). A dynamical study of the two subclouds points out the existence of a
group of star-forming galaxies infalling into the core of the South-East
subcloud and suggests that two other groups are infalling into the NW and SE
subclusters respectively. These three subgroups contain a higher fraction of
star-forming galaxies than the cluster core, as expected during merging events.
Abell 1367 appears as a young cluster currently forming at the intersection of
two filaments.Comment: 15 pages, 13 figures, 7 tables. Accepted for publication on A&A. High
resolution figures at http://goldmine.mib.infn.it/papers/a1367.htm
Special Massive Spin-2 on de Sitter Space
The theory of a massive spin-2 state on the de Sitter space -- with the mass
squared equal to one sixth of the curvature -- is special for two reasons: (i)
it exhibits an enhanced local symmetry; (ii) it emerges as a part of the model
that gives rise to the self-accelerated Universe. The known problems of this
theory are: either it cannot be coupled to a non-conformal conserved
stress-tensor because of the enhanced symmetry, or it propagates a ghost-like
state when the symmetry is constrained by the Lagrange multiplier method. Here
we propose a solution to these problems in the linearized approximation.Comment: 9 pages, reference added, JCAP versio
Capital costs in tidal stream energy projects - A spatial approach
Tidal stream energy projects involve high amounts of capital, for which ex-ante economic assessments are crucial. Unfortunately, the existing models to estimate the capital costs of a tidal stream energy project are often oversimplified. Focused on single estimates on a per installed power basis, such models fail to capture the all-important sensitivity of the capital costs to project site-specific characteristics (water depth, distance to the shoreline, etc.) The objective of this work is twofold: (1) to develop a new formulation for estimating the capital costs of a tidal stream farm, and (2) to implement this formula in a Matlab-based tool coupled with a Navier-Stokes solver and thus deliver the spatial distribution of this cost. As a case study, the new tool is applied to the Bristol Channel - the single largest resource area for tidal energy in the UK. Here, the best sites to install tidal stream farms are identified, with a cost comparable to that of offshore wind energy. Simulation results show that the proposed method is more efficient than the existing approaches. The results of this work have relevant policy implications in that they serve as decision criteria for allocating tidal stream projects and for designating supporting mechanisms
Reynolds number and Shallow Depth Sloshing
The dependence on the Reynolds number of shallow depth sloshing ïŹows inside rectangular tanks subjected to forced harmonic motion is studied in this paper with weakly compressible SPH. We are interested in assessing the in ïŹuenceof viscous effects on the dynamics of shallow depth sloshing ïŹows by using an SPH solver and by comparing with a Navier-Stokes level-set solver results. The goal of trying to model these viscous ïŹows is compromised by the resolution requested due to their Reynolds number, if boundary layer effects are to be modeled. The convenience and feasibility of the implementation of free-slip and no-slip boundary conditions is also discusse
Convolutional Goppa Codes
We define Convolutional Goppa Codes over algebraic curves and construct their
corresponding dual codes. Examples over the projective line and over elliptic
curves are described, obtaining in particular some Maximum-Distance Separable
(MDS) convolutional codes.Comment: 8 pages, submitted to IEEE Trans. Inform. Theor
- âŠ