1,114 research outputs found
Generation of decoherence-free displaced squeezed states of radiation fields and a squeezed reservoir for atoms in cavity QED
We present a way to engineer an effective anti-Jaynes-Cumming and a
Jaynes-Cumming interaction between an atomic system and a single cavity mode
and show how to employ it in reservoir engineering processes. To construct the
effective Hamiltonian, we analyse considered the interaction of an atomic
system in a \{Lambda} configuration, driven by classical fields, with a single
cavity mode. With this interaction, we firstly show how to generate a
decoherence-free displaced squeezed state for the cavity field. In our scheme,
an atomic beam works as a reservoir for the radiation field trapped inside the
cavity, as employed recently by S. Pielawa et al. [Phys. Rev. Lett. 98, 240401
(2007)] to generate an Einstein-Podolsky-Rosen entangled radiation state in
high-Q resonators. In our scheme, all the atoms have to be prepared in the
ground state and, as in the cited article, neither atomic detection nor precise
interaction times between the atoms and the cavity mode are required. From this
same interaction, we can also generate an ideal squeezed reservoir for atomic
systems. For this purpose we have to assume, besides the engineered atom-field
interaction, a strong decay of the cavity field (i.e., the cavity decay must be
much stronger than the effective atom-field coupling). With this scheme, some
interesting effects in the dynamics of an atom in a squeezed reservoir could be
tested
The Tulczyjew triple for classical fields
The geometrical structure known as the Tulczyjew triple has proved to be very
useful in describing mechanical systems, even those with singular Lagrangians
or subject to constraints. Starting from basic concepts of variational
calculus, we construct the Tulczyjew triple for first-order Field Theory. The
important feature of our approach is that we do not postulate {\it ad hoc} the
ingredients of the theory, but obtain them as unavoidable consequences of the
variational calculus. This picture of Field Theory is covariant and complete,
containing not only the Lagrangian formalism and Euler-Lagrange equations but
also the phase space, the phase dynamics and the Hamiltonian formalism. Since
the configuration space turns out to be an affine bundle, we have to use affine
geometry, in particular the notion of the affine duality. In our formulation,
the two maps and which constitute the Tulczyjew triple are
morphisms of double structures of affine-vector bundles. We discuss also the
Legendre transformation, i.e. the transition between the Lagrangian and the
Hamiltonian formulation of the first-order field theor
Long-term observations minus background monitoring of ground-based brightness temperatures from a microwave radiometer network
Abstract. Ground-based microwave radiometers (MWRs) offer the capability to provide continuous, high-temporal-resolution observations of the atmospheric thermodynamic state in the planetary boundary layer (PBL) with low maintenance. This makes MWR an ideal instrument to supplement radiosonde and satellite observations when initializing numerical weather prediction (NWP) models through data assimilation. State-of-the-art data assimilation systems (e.g. variational schemes) require an accurate representation of the differences between model (background) and observations, which are then weighted by their respective errors to provide the best analysis of the true atmospheric state. In this perspective, one source of information is contained in the statistics of the differences between observations and their background counterparts (O–B). Monitoring of O–B statistics is crucial to detect and remove systematic errors coming from the measurements, the observation operator, and/or the NWP model. This work illustrates a 1-year O–B analysis for MWR observations in clear-sky conditions for an European-wide network of six MWRs. Observations include MWR brightness temperatures (TB) measured by the two most common types of MWR instruments. Background profiles are extracted from the French convective-scale model AROME-France before being converted into TB. The observation operator used to map atmospheric profiles into TB is the fast radiative transfer model RTTOV-gb. It is shown that O–B monitoring can effectively detect instrument malfunctions. O–B statistics (bias, standard deviation, and root mean square) for water vapour channels (22.24–30.0 GHz) are quite consistent for all the instrumental sites, decreasing from the 22.24 GHz line centre ( ∼ 2–2.5 K) towards the high-frequency wing ( ∼ 0.8–1.3 K). Statistics for zenith and lower-elevation observations show a similar trend, though values increase with increasing air mass. O–B statistics for temperature channels show different behaviour for relatively transparent (51–53 GHz) and opaque channels (54–58 GHz). Opaque channels show lower uncertainties (< 0.8–0.9 K) and little variation with elevation angle. Transparent channels show larger biases ( ∼ 2–3 K) with relatively low standard deviations ( ∼ 1–1.5 K). The observations minus analysis TB statistics are similar to the O–B statistics, suggesting a possible improvement to be expected by assimilating MWR TB into NWP models. Lastly, the O–B TB differences have been evaluated to verify the normal-distribution hypothesis underlying variational and ensemble Kalman filter-based DA systems. Absolute values of excess kurtosis and skewness are generally within 1 and 0.5, respectively, for all instrumental sites, demonstrating O–B normal distribution for most of the channels and elevations angles
Social Enterprise in Spain: A Diversity of Roots and a Proposal of Models
The term “social enterprise” was first used, at the end of the 1980s, by organisations that promoted the social and labour integration of persons at risk of social and labour exclusion and other similar social activities. The social economy sector has since slowly introduced this term to describe its entities in order to gain recognition by society, and it is working to promote a generally accepted definition of social enterprise’s behaviour based on the principles and values of the social economy (participation, general interest...). According to Article 5 of Spanish Law 5/2011 on the Social Economy, work integration social enterprises and so-called “special employment centres” are part of the social economy, and so are all firms and entities carrying out activities following the values and principles of the social economy sector.
In this context, organisations of the social economy sector also are beginning to use the “social enterprise” concept. In Spain, a debate still exists regarding its exact definition. A mix of perspectives on this concept, with different nuances, can be observed. Besides, the current context of reduced governmental budgets and social services in Spain causes social organisations to adopt new approaches to this term of social enterprise, as this type of organisation is more likely to receive funds from the European Union.
This paper’s objective is to analyse all perspectives on the concept of social enterprise as well as the various social enterprise models existing in Spain. The document structure is organized as follow. In the first section, we present the context and the main concepts related to social enterprises in this country. In the second section, we provide an analysis of changes in the evolution of social enterprise criteria to identify established models and emerging patterns. In the third section, we put forward another typology, based on institutionalisation stages. Finally, we conclude by recommending an approach to future work and provide a basic bibliography on the subject
Axiomatic geometric formulation of electromagnetism with only one axiom: the field equation for the bivector field F with an explanation of the Trouton-Noble experiment
In this paper we present an axiomatic, geometric, formulation of
electromagnetism with only one axiom: the field equation for the Faraday
bivector field F. This formulation with F field is a self-contained, complete
and consistent formulation that dispenses with either electric and magnetic
fields or the electromagnetic potentials. All physical quantities are defined
without reference frames, the absolute quantities, i.e., they are geometric
four dimensional (4D) quantities or, when some basis is introduced, every
quantity is represented as a 4D coordinate-based geometric quantity comprising
both components and a basis. The new observer independent expressions for the
stress-energy vector T(n)(1-vector), the energy density U (scalar), the
Poynting vector S and the momentum density g (1-vectors), the angular momentum
density M (bivector) and the Lorentz force K (1-vector) are directly derived
from the field equation for F. The local conservation laws are also directly
derived from that field equation. The 1-vector Lagrangian with the F field as a
4D absolute quantity is presented; the interaction term is written in terms of
F and not, as usual, in terms of A. It is shown that this geometric formulation
is in a full agreement with the Trouton-Noble experiment.Comment: 32 pages, LaTex, this changed version will be published in Found.
Phys. Let
Synthesis of Non-uniformly Correlated Partially Coherent Sources Using a Deformable Mirror
The near real-time synthesis of a non-uniformly correlated partially coherent source using a low-actuator-count deformable mirror is demonstrated. The statistical optics theory underpinning the synthesis method is reviewed. The experimental results of a non-uniformly correlated source are presented and compared to theoretical predictions. A discussion on how deformable mirror characteristics such as actuator count and pitch affect source generation is also included
High Redshift X-Ray Selected Quasars: CXOCY J125304.0-090737 joins the club
We present a new X-ray selected high redshift quasar CXOCY J125304.0-090737
at z=4.179, discovered by the Calan-Yale Deep Extragalactic Research (CYDER)
Survey. This quasar is the fifth X-ray selected high redshift radio quiet
quasar () found so far. Here, we present its observed properties which are
characterized by its relative optical and X-ray faintness, its X-ray hardness
and its X-ray strength compared to optically selected quasars at high redshift.
We also compare the X-ray selected high redshift radio quiet quasars to their
optically selected counterparts. We find that the optical to X-ray spectral
slope, , is statistically harder (more X-ray luminous) for the
X-ray selected radio quiet quasars than for the optically selected ones. This
result, given the different range of rest frame ultraviolet luminosities
studied and the selection of the samples, is consistent with the previously
found correlation between X-ray and rest frame ultraviolet luminosities and
would extend that result to a much wider luminosity range at high redshift.
Finally, we discuss the prospects of unveiling the quasar luminosity function
at high redshifts using X-ray surveys. The discovery of a high redshift object
in the first field of our survey program provides suggestive evidence that
X-ray selected surveys may identify more such objects than would be expected
from an extrapolation of the optical luminosity function.Comment: AJ accepted, 19 pages including 6 figure
Galactic Collapse of Scalar Field Dark Matter
We present a scenario for galaxy formation based on the hypothesis of scalar
field dark matter. We interpret galaxy formation through the collapse of a
scalar field fluctuation. We find that a cosh potential for the
self-interaction of the scalar field provides a reasonable scenario for
galactic formation, which is in agreement with cosmological observations and
phenomenological studies in galaxies.Comment: 4 pages, 3 figue
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