1,245 research outputs found
Estimating the Uncertainty in Population Projections by Resampling Methods
This paper proposes a new approach to introducing quantitatively measured uncertainty into population projections. It is to a lesser degree based on past time-series than other approaches, since it uses random walk models for migration, mortality and fertility, for which upper and lower bounds are defined. No parametric distribution is fitted to the observations, but the random walk is resampled from the past data. By putting bounds on the level that fertility can reach in the future, further substantive information is introduced that transcends the information derived from the observed time series. By sampling 10.000 path of the random walks in fertility, mortality and migration, the distributions of population size and structure up to 2050 for Austria, Mauritius and USA are estimated
Clustering-Based Materialized View Selection in Data Warehouses
Materialized view selection is a non-trivial task. Hence, its complexity must
be reduced. A judicious choice of views must be cost-driven and influenced by
the workload experienced by the system. In this paper, we propose a framework
for materialized view selection that exploits a data mining technique
(clustering), in order to determine clusters of similar queries. We also
propose a view merging algorithm that builds a set of candidate views, as well
as a greedy process for selecting a set of views to materialize. This selection
is based on cost models that evaluate the cost of accessing data using views
and the cost of storing these views. To validate our strategy, we executed a
workload of decision-support queries on a test data warehouse, with and without
using our strategy. Our experimental results demonstrate its efficiency, even
when storage space is limited
Entropy Production in a Persistent Random Walk
We consider a one-dimensional persisent random walk viewed as a deterministic
process with a form of time reversal symmetry. Particle reservoirs placed at
both ends of the system induce a density current which drives the system out of
equilibrium. The phase space distribution is singular in the stationary state
and has a cumulative form expressed in terms of generalized Takagi functions.
The entropy production rate is computed using the coarse-graining formalism of
Gaspard, Gilbert and Dorfman. In the continuum limit, we show that the value of
the entropy production rate is independent of the coarse-graining and agrees
with the phenomenological entropy production rate of irreversible
thermodynamics.Comment: 21 pages, 8 figures, to appear in Physica
History repeats? : the rise of the new middle classes in the developing world
1.
Although the ability to detect chemical cues is widespread in many organisms, it is surprising how
little is known about the role of chemical communication in avian life histories. Nowadays, growing
evidence suggests that birds can use olfaction in several contexts. However, we still do not know the
role of bird olfaction in one of the most important determinants of survival, predator detection.
2.
Blue tits,
Cyanistes caeruleus
L., were exposed to chemical cues of: (i) mustelid (predator), (ii) quail
(odorous control); or (iii) water (odourless control) inside the nest-box where they were provisioning
8-day-old nestlings.
3.
We show that blue tits were able to detect the chemical cues and showed antipredatory behaviours
to cope with the risk of predation. Birds delayed their entry to the nest-box, and they perched on the
hole of the nest-box and refused to enter more times when they found predator scent than control
scents inside the nest-box. In addition, birds decreased the time spent inside the predator-scented
nest-box when feeding nestlings.
4.
The discovery of the ability of birds to use chemical cues of predators to accurately assess predation
may help to understand many aspects of bird life histories that have been neglected until now.Peer reviewe
Geometrical locus of massive test particle orbits in the space of physical parameters in Kerr space-time
Gravitational radiation of binary systems can be studied by using the
adiabatic approximation in General Relativity. In this approach a small
astrophysical object follows a trajectory consisting of a chained series of
bounded geodesics (orbits) in the outer region of a Kerr Black Hole,
representing the space time created by a bigger object. In our paper we study
the entire class of orbits, both of constant radius (spherical orbits), as well
as non-null eccentricity orbits, showing a number of properties on the physical
parameters and trajectories. The main result is the determination of the
geometrical locus of all the orbits in the space of physical parameters in Kerr
space-time. This becomes a powerful tool to know if different orbits can be
connected by a continuous change of their physical parameters. A discussion on
the influence of different values of the angular momentum of the hole is given.
Main results have been obtained by analytical methods.Comment: 26 pages, 12 figure
Input-output theory for fermions in an atom cavity
We generalize the quantum optical input-output theory developed for optical
cavities to ultracold fermionic atoms confined in a trapping potential, which
forms an "atom cavity". In order to account for the Pauli exclusion principle,
quantum Langevin equations for all cavity modes are derived. The dissipative
part of these multi-mode Langevin equations includes a coupling between cavity
modes. We also derive a set of boundary conditions for the Fermi field that
relate the output fields to the input fields and the field radiated by the
cavity. Starting from a constant uniform current of fermions incident on one
side of the cavity, we use the boundary conditions to calculate the occupation
numbers and current density for the fermions that are reflected and transmitted
by the cavity
Extremal black holes in D=5: SUSY vs. Gauss-Bonnet corrections
We analyse near-horizon solutions and compare the results for the black hole
entropy of five-dimensional spherically symmetric extremal black holes when the
N=2 SUGRA actions are supplied with two different types of higher-order
corrections: (1) supersymmetric completion of gravitational Chern-Simons term,
and (2) Gauss-Bonnet term. We show that for large BPS black holes lowest order
\alpha' corrections to the entropy are the same, but for non-BPS are generally
different. We pay special attention to the class of prepotentials connected
with K3\times T^2 and T^6 compactifications. For supersymmetric correction we
find beside BPS also a set of non-BPS solutions. In the particular case of T^6
compactification (equivalent to the heterotic string on ) we
find the (almost) complete set of solutions (with exception of some non-BPS
small black holes), and show that entropy of small black holes is different
from statistical entropy obtained by counting of microstates of heterotic
string theory. We also find complete set of solutions for K3\times T^2 and T^6
case when correction is given by Gauss-Bonnet term. Contrary to
four-dimensional case, obtained entropy is different from the one with
supersymmetric correction. We show that in Gauss-Bonnet case entropy of small
``BPS'' black holes agrees with microscopic entropy in the known cases.Comment: 28 pages; minor changes, version to appear in JHE
The Dipole Coupling of Atoms and Light in Gravitational Fields
The dipole coupling term between a system of N particles with total charge
zero and the electromagnetic field is derived in the presence of a weak
gravitational field. It is shown that the form of the coupling remains the same
as in flat space-time if it is written with respect to the proper time of the
observer and to the measurable field components. Some remarks concerning the
connection between the minimal and the dipole coupling are given.Comment: 10 pages, LaTe
Higher-order mutual coherence of optical and matter waves
We use an operational approach to discuss ways to measure the higher-order
cross-correlations between optical and matter-wave fields. We pay particular
attention to the fact that atomic fields actually consist of composite
particles that can easily be separated into their basic constituents by a
detection process such as photoionization. In the case of bosonic fields, that
we specifically consider here, this leads to the appearance in the detection
signal of exchange contributions due to both the composite bosonic field and
its individual fermionic constituents. We also show how time-gated counting
schemes allow to isolate specific contributions to the signal, in particular
involving different orderings of the Schr\"odinger and Maxwell fields.Comment: 11 pages, 2 figure
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