220 research outputs found
Phase space path integral in curved space
Phase space path integral is worked out in a riemannian geometry, by
employing a prescription for the infinitesimal propagator that takes riemannian
normal coordinates and momenta on an equal footing. The operator ordering
induced by this prescription leads to the DeWitt curvature coupling in the
Schrodinger equation.Comment: 11 page
Chern-Simons action for inhomogeneous Virasoro group as an extension of three dimensional flat gravity
We initiate the study of a Chern-Simons action associated to the semi-direct
sum of the Virasoro algebra with its coadjoint representation. This model
extends the standard Chern-Simons formulation of three dimensional flat gravity
and is similar to the higher-spin extension of three dimensional anti-de Sitter
or flat gravity. The extension can also be constructed for the exotic but not
for the cosmological constant deformation of flat gravity.Comment: 15 pages. Version to appear in J. of Math. Phy
Effect of the alien invasive bivalve Corbicula fluminea on the nutrient dynamics under climate change scenarios
The main aim of this study was to evaluate the impact of the alien invasive bivalve Corbicula fluminea (Müller, 1774) in the nutrient dynamics of temperate estuarine systems (oligohaline areas) under climate change scenarios.
The scenarios simulated shifts in climatic conditions, following salinity (0 or 5) and temperature (24 or 30 °C) changes, usual during drought and heat wave events. The effect of the individual size/age (different size classes with fixed biomass) and density (various densities of <1 cm clams) on the bioturbation-associated nutrient dynamics were also evaluated under an 18-day laboratory experimental setup.
Results highlight the significant effect of C. fluminea on the ecosystem nutrient dynamics, enhancing the efflux of both phosphate and dissolved inorganic nitrogen (DIN) from the sediments to the water column. Both drought and heat wave events will have an impact on the DIN dynamics within C. fluminea colonized systems, favouring a higher NH4-N efflux.
The population structure of C. fluminea will have a decisive role on the impact of the species, with stronger nutrient effluxes associated with a predominantly juvenile population structure.publishe
Complete Calabi-Yau metrics from Kahler metrics in D=4
In the present work the local form of certain Calabi-Yau metrics possessing a
local Hamiltonian Killing vector is described in terms of a single non linear
equation. The main assumptions are that the complex -form is of the form
, where is preserved by the Killing
vector, and that the space of the orbits of the Killing vector is, for fixed
value of the momentum map coordinate, a complex 4-manifold, in such a way that
the complex structure of the 4-manifold is part of the complex structure of the
complex 3-fold. The link with the solution generating techniques of [26]-[28]
is made explicit and in particular an example with holonomy exactly SU(3) is
found by use of the linearization of [26], which was found in the context of D6
branes wrapping a holomorphic 1-fold in a hyperkahler manifold. But the main
improvement of the present method, unlike the ones presented in [26]-[28], does
not rely in an initial hyperkahler structure. Additionally the complications
when dealing with non linear operators over the curved hyperkahler space are
avoided by use of this method.Comment: Version accepted for publication in Phys.Rev.
Geometric Configurations, Regular Subalgebras of E10 and M-Theory Cosmology
We re-examine previously found cosmological solutions to eleven-dimensional
supergravity in the light of the E_{10}-approach to M-theory. We focus on the
solutions with non zero electric field determined by geometric configurations
(n_m, g_3), n\leq 10. We show that these solutions are associated with rank
regular subalgebras of E_{10}, the Dynkin diagrams of which are the (line)
incidence diagrams of the geometric configurations. Our analysis provides as a
byproduct an interesting class of rank-10 Coxeter subgroups of the Weyl group
of E_{10}.Comment: 48 pages, 27 figures, 5 tables, references added, typos correcte
Information vs Engagement in parliamentary websites – a case study of Brazil and the UK
Parliamentary websites have become the main window of parliament to the outside world. More than a gimmick, they are an essential element in the promotion of a relationship between parliament and citizens. This paper develops a comparative analysis of the websites of the lower chambers of the Brazilian and the British parliaments, respectively the Chamber of Deputies and the House of Commons. We structure this analysis around three dimensions: 1) information about the institution; 2) information about parliamentary activity; and 3) tools to promote engagement with the public. The choice of two very different case studies enables us to consider more clearly the specific purposes of these parliamentary websites. We consider in particular if these parliaments' institutional differences affect their websites. The websites' analysis is complemented by semi-structured elite interviews with parliamentary staff who manage the services provided by these websites. Our analysis shows that both websites achieve much higher levels of complexity in the information area than in engagement. But it also shows that the Brazilian parliament website includes far more tools designed for public interaction than its UK counterpart. The indexes and interviews show that both institutions are highly committed to disseminating data and information to citizens. This is seen as a path towards achieving higher accountability and improving knowledge about parliamentary processes and, consequently, improving public image and levels of trust. Whilst there is a strong focus on the provision of information, there is still little evidence of enabling citizen participation in the legislative process. This is partly due to a tension between conceptions of representative democracy and those of participatory democracy. The articulation between these different types of democracy still has a long way to be resolved, although parliaments are slowly introducing participatory tools
Thermal Correlators in Holographic Models with Lifshitz scaling
We study finite temperature effects in two distinct holographic models that
exhibit Lifshitz scaling, looking to identify model independent features in the
dual strong coupling physics. We consider the thermodynamics of black branes
and find different low-temperature behavior of the specific heat. Deformation
away from criticality leads to non-trivial temperature dependence of
correlation functions and we study how the characteristic length scale in the
two point function of scalar operators varies as a function of temperature and
deformation parameters.Comment: 28 pages, 8 figures; typos corrected, references added, published
versio
On higher derivative gravity, c-theorems and cosmology
We consider higher derivative gravity lagrangians in 3 and 4 dimensions,
which admit simple c-theorems, including upto six derivative curvature
invariants. Following a suggestion by Myers, these lagrangians are restricted
such that the fluctuations around (anti) de Sitter spaces have second order
linearized equations of motion. We study c-theorems both in the context of
AdS/CFT and cosmology. In the context of cosmology, the monotonic function is
the entropy defined on the apparent horizon through Wald's formula. Exact black
hole solutions which are asymptotically (anti) de Sitter are presented. An
interesting lower bound for entropy is found in de Sitter space. Some aspects
of cosmology in both D=3 and D=4 are discussed.Comment: 23 pages, v3: clarifications added, references adde
Election proximity and representation focus in party-constrained environments
Do elected representatives have a time-constant representation focus or do they adapt their focus depending on election proximity? In this article, we examine these overlooked theoretical and empirical puzzles by looking at how reelection-seeking actors adapt their legislative behavior according to the electoral cycle. In parliamentary democracies, representatives need to serve two competing principals: their party and their district. Our analysis hinges on how representatives make a strategic use of parliamentary written questions in a highly party-constrained institutional context to heighten their reselection and reelection prospects. Using an original data set of over 32,000 parliamentary questions tabled by Portuguese representatives from 2005 to 2015, we examine how time interacts with two key explanatory elements: electoral vulnerability and party size. Results show that representation focus is not static over time and, in addition, that electoral vulnerability and party size shape strategic use of parliamentary questions
- …