561 research outputs found
Acoustics of Modern and Old Museums
The goal of this study is to acoustically characterize typical modern and old museums. Modern museums can easily have a bad acoustic behavior due to the widespread use of very smooth and reflective coatings, hard floors, high-ceilings and very expressive volumes. This situation is not usually seen in "old" museums. Acoustic analyses of two case-studies (the 1999 Contemporary Art Museum of Serralves and the National Museum of Soares dos Reis, in Porto, Portugal) are held using objective parameters measured in situ in their largest showrooms (RT, RASTI, LAeq background noise HVAC and NC/NR). This work studies the generic acoustic requirements of these buildings and recommends optimal values for those parameters. Some proposals for the acoustical improvement in the main rooms are suggested. A short comparison of results with other museums is shown
Vortex phase diagram in trapped Bose-Einstein condensation
The vortex phase diagram in the external rotation frequency versus
temperature is calculated for dilute Bose-Einstein condensed gases. It is
determined within the Bogoliubov-Popov theory for a finite temperature where
the condensate and non-condensate fractions are treated in an equal footing.
The temperature dependences of various thermodynamic instability lines for the
vortex nucleation are computed to construct the phase diagram. Experiments are
proposed to resolve a recent controversy on the vortex creation problem
associated with the quantized vortex observation in Rb atom gases.Comment: 11 pages, 8 figure
Nonlinear waves in a cylindrical Bose-Einstein condensate
We present a complete calculation of solitary waves propagating in a steady
state with constant velocity v along a cigar-shaped Bose-Einstein trap
approximated as infinitely-long cylindrical. For sufficiently weak couplings
(densities) the main features of the calculated solitons could be captured by
effective one-dimensional (1D) models. However, for stronger couplings of
practical interest, the relevant solitary waves are found to be hybrids of
quasi-1D solitons and 3D vortex rings. An interesting hierarchy of vortex rings
occurs as the effective coupling constant is increased through a sequence of
critical values. The energy-momentum dispersion of the above structures is
shown to exhibit characteristics similar to a mode proposed sometime ago by
Lieb within a strictly 1D model, as well as some rotonlike features.Comment: 10 pages, 12 figure
3D heterotic string theory: new approach and extremal solutions
We develop a new formalism for the bosonic sector of low-energy heterotic
string theory toroidally compactified to three dimensions. This formalism is
based on the use of some single non-quadratic real matrix potential which
transforms linearly under the action of subgroup of the three-dimensional
charging symmetries. We formulate a new charging symmetry invariant approach
for the symmetry generation and straightforward construction of asymptotically
flat solutions. Finally, using the developed approach and the established
formal analogy between the heterotic and Einstein-Maxwell theories, we
construct a general class of the heterotic string theory extremal solutions of
the Israel-Wilson-Perjes type. This class is asymptotically flat and charging
symmetry complete; it includes the extremal solutions constructed before and
possesses the non-trivial bosonic string theory limit.Comment: 20 pages in Late
The Global Forest Transition as a Human Affair
Forests across the world stand at a crossroads where climate and land-use changes are shaping their future. Despite demonstrations of political will and global efforts, forest loss, fragmentation, and degradation continue unabated. No clear evidence exists to suggest that these initiatives are working. A key reason for this apparent ineffectiveness could lie in the failure to recognize the agency of all stakeholders involved. Landscapes do not happen. We shape them. Forest transitions are social and behavioral before they are ecological. Decision makers need to integrate better representations of people’s agency in their mental models. A possible pathway to overcome this barrier involves eliciting mental models behind policy decisions to allow better representation of human agency, changing perspectives to better understand divergent points of view, and refining strategies through explicit theories of change. Games can help decision makers in all of these tasks
Gauge and Scheme Dependence of Mixing Matrix Renormalization
We revisit the issue of mixing matrix renormalization in theories that
include Dirac or Majorana fermions. We show how a gauge-variant on-shell
renormalized mixing matrix can be related to a manifestly gauge-independent one
within a generalized scheme of renormalization. This
scheme-dependent relation is a consequence of the fact that in any scheme of
renormalization, the gauge-dependent part of the mixing-matrix counterterm is
ultra-violet safe and has a pure dispersive form. Employing the unitarity
properties of the theory, we can successfully utilize the afore-mentioned
scheme-dependent relation to preserve basic global or local symmetries of the
bare Lagrangian through the entire process of renormalization. As an immediate
application of our study, we derive the gauge-independent renormalization-group
equations of mixing matrices in a minimal extension of the Standard Model with
isosinglet neutrinos.Comment: 31 pages, LaTeX, uses axodraw.st
Categorizing Different Approaches to the Cosmological Constant Problem
We have found that proposals addressing the old cosmological constant problem
come in various categories. The aim of this paper is to identify as many
different, credible mechanisms as possible and to provide them with a code for
future reference. We find that they all can be classified into five different
schemes of which we indicate the advantages and drawbacks.
Besides, we add a new approach based on a symmetry principle mapping real to
imaginary spacetime.Comment: updated version, accepted for publicatio
Generic thin-shell gravastars
We construct generic spherically symmetric thin-shell gravastars by using the
cut-and-paste procedure. We take considerable effort to make the analysis as
general and unified as practicable; investigating both the internal physics of
the transition layer and its interaction with "external forces" arising due to
interactions between the transition layer and the bulk spacetime. Furthermore,
we discuss both the dynamic and static situations. In particular, we consider
"bounded excursion" dynamical configurations, and probe the stability of static
configurations. For gravastars there is always a particularly compelling
configuration in which the surface energy density is zero, while surface
tension is nonzero.Comment: V1: 39 pages, 9 figures; V2: 40 pages, 9 figures. References added,
some discussion added, some typos fixed. Identical to published version.
arXiv admin note: text overlap with arXiv:1112.205
Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory
Data from the Pierre Auger Observatory are analyzed to search for
anisotropies near the direction of the Galactic Centre at EeV energies. The
exposure of the surface array in this part of the sky is already significantly
larger than that of the fore-runner experiments. Our results do not support
previous findings of localized excesses in the AGASA and SUGAR data. We set an
upper bound on a point-like flux of cosmic rays arriving from the Galactic
Centre which excludes several scenarios predicting sources of EeV neutrons from
Sagittarius . Also the events detected simultaneously by the surface and
fluorescence detectors (the `hybrid' data set), which have better pointing
accuracy but are less numerous than those of the surface array alone, do not
show any significant localized excess from this direction.Comment: Matches published versio
Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter
Data collected by the Pierre Auger Observatory through 31 August 2007 showed
evidence for anisotropy in the arrival directions of cosmic rays above the
Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{eV}. The
anisotropy was measured by the fraction of arrival directions that are less
than from the position of an active galactic nucleus within 75 Mpc
(using the V\'eron-Cetty and V\'eron catalog). An updated
measurement of this fraction is reported here using the arrival directions of
cosmic rays recorded above the same energy threshold through 31 December 2009.
The number of arrival directions has increased from 27 to 69, allowing a more
precise measurement. The correlating fraction is , compared
with expected for isotropic cosmic rays. This is down from the early
estimate of . The enlarged set of arrival directions is
examined also in relation to other populations of nearby extragalactic objects:
galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in
hard X-rays by the Swift Burst Alert Telescope. A celestial region around the
position of the radiogalaxy Cen A has the largest excess of arrival directions
relative to isotropic expectations. The 2-point autocorrelation function is
shown for the enlarged set of arrival directions and compared to the isotropic
expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201
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