20,696 research outputs found
Geometry of D1-D5-P bound states
Supersymmetric solutions of 6-d supergravity (with two translation
symmetries) can be written as a hyperkahler base times a 2-D fiber. The subset
of these solutions which correspond to true bound states of D1-D5-P charges
give microstates of the 3-charge extremal black hole. To understand the
characteristics shared by the bound states we decompose known bound state
geometries into base-fiber form. The axial symmetry of the solutions make the
base Gibbons-Hawking. We find the base to be actually `pseudo-hyperkahler': The
signature changes from (4,0) to (0,4) across a hypersurface. 2-charge D1-D5
geometries are characterized by a `central curve' ; the analogue for
3-charge appears to be a hypersurface that for our metrics is an orbifold of
.Comment: 20 pages, LaTeX; references adde
Marcatili's Lossless Tapers and Bends: an Apparent Paradox and its Solution
Numerical results based on an extended BPM algorithm indicate that, in
Marcatili's lossless tapers and bends, through-flowing waves are drastically
different from standing waves. The source of this surprising behavior is
inherent in Maxwell's equations. Indeed, if the magnetic field is correctly
derived from the electric one, and the Poynting vector is calculated, then the
analytical results are reconciled with the numerical ones. Similar
considerations are shown to apply to Gaussian beams in free space.Comment: 4 pages, figures include
Diffuse light in z~0.25 galaxy clusters: constraining tidal damage and the faint end of the Luminosity Function
The starlight coming from the intergalactic space in galaxy clusters and
groups witnesses the violent tidal interactions that galaxies experience in
these dense environments. Such interactions may be (at least partly)
responsible for the transformation of normal star-forming galaxies into passive
dwarf ellipticals (dEs). In this contribution we present the first systematic
study of the IntraCluster Light (ICL) for a statistically representative sample
(Zibetti et al. 2005), which comprises 683 clusters selected between z=0.2 and
0.3 from ~1500 deg^2 in the SDSS. Their ICL is studied by stacking the images
in the g-, r-, and i-band after masking out all galaxies and polluting sources.
In this way a very uniform background illumination is obtained, that allows us
to measure surface brightnesses as faint as 31 mag/arcsec^2 and to trace the
ICL out to 700 kpc from the central galaxy. We find that the local fraction of
light contributed by intracluster stars rapidly decreases as a function of the
clustercentric distance, from ~40% at 100 kpc to ~5% at 500 kpc. By comparing
the distribution and colours of the ICL and of the clusters galaxies, we find
indication that the main source of ICL are the stars stripped from galaxies
that plunge deeply into the cluster potential well along radial orbits. Thus,
if dEs are the remnants of these stripped progenitors we should expect similar
radial orbital anisotropies and correlations between the dE luminosity function
and the amount of ICL in different clusters. The diffuse emission we measure is
contaminated by faint unresolved galaxies: this makes our flux estimate depend
to some extent on the assumed luminosity function, but, on the other hand,
allows us to constrain the number of faint galaxies. Our present results
disfavour steep (alpha<-1.35) faint-end powerlaw slopes.Comment: 4 pages, 2 figures, use iauc.cls. Oral presentation to appear in the
proceedings of "IAU Colloquium 198 - Near-Field Cosmology with Dwarf
Elliptical Galaxies", Les Diablerets 14-18 March 2005, B. Binggeli and H.
Jerjen ed
Improving building energy efficiency: case study
The main purpose of this study was to conduct a study for improving energy efficiency of an important building in Rome, the Headquarters of the Italian State Monopoly. The study was conducted by comparing conventional analysis tools with innovative ones, in order to evaluate the possible solutions, both structural and plant, aimed at the use of renewable sources and at energy saving. After making a thermo graphic survey, the first and useful step for a good energy audit, conduct building energy was simulated, at first in steady state by the use of a software widely used at the professional level, then in transient state by the use of TRNSYS, a finite difference method software which is able to simulate more accurately conduct building energy. The next step was to propose possible redevelopment of a structural and energy plant that promotes the building energy rating higher, finding the right balance between the energetic and economic aspect. Among the interventions plant, two possible workarounds have been proposed and designed in detail:
- installation of a photovoltaic system;
- installation of a solar cooling system.
Both solutions lead to a reduction of electricity consumption with a significant impact in economic and environmental term
Sterilizable Liquid Propulsion System, Part 1 Final Report, 5 Oct. 1966 - 31 Mar. 1968
Exposure of assembled and fueled bipropellant liquid propulsion system to ethylene oxid
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