13,393 research outputs found
Shape-from-intrinsic operator
Shape-from-X is an important class of problems in the fields of geometry
processing, computer graphics, and vision, attempting to recover the structure
of a shape from some observations. In this paper, we formulate the problem of
shape-from-operator (SfO), recovering an embedding of a mesh from intrinsic
differential operators defined on the mesh. Particularly interesting instances
of our SfO problem include synthesis of shape analogies, shape-from-Laplacian
reconstruction, and shape exaggeration. Numerically, we approach the SfO
problem by splitting it into two optimization sub-problems that are applied in
an alternating scheme: metric-from-operator (reconstruction of the discrete
metric from the intrinsic operator) and embedding-from-metric (finding a shape
embedding that would realize a given metric, a setting of the multidimensional
scaling problem)
fluxes and exotic branes
We consider the superpotential generated in type-II orientifold
models by non-geometric fluxes. In particular, we focus on the family of
fluxes, that are related by T-duality transformations to the S-dual of the
flux. We determine the general rule that transforms a given flux in this family
under a single T-duality transformation. This rule allows to derive a complete
expression for the superpotential for both the IIA and the IIB theory for the
particular case of a orientifold. We
then consider how these fluxes modify the generalised Bianchi identities. In
particular, we derive a fully consistent set of quadratic constraints coming
from the NS-NS Bianchi identities. On the other hand, the flux Bianchi
identities induce tadpoles, and we determine a set of exotic branes that can be
consistently included in order to cancel them. This is achieved by determining
a universal transformation rule under T-duality satisfied by all the branes in
string theory.Comment: 29 pages. Refs. added, end of subsection 4.2 improved, other minor
changes. Version published on JHE
Quantum discord for general two--qubit states: Analytical progress
We present a reliable algorithm to evaluate quantum discord for general
two--qubit states, amending and extending an approach recently put forward for
the subclass of X--states. A closed expression for the discord of arbitrary
states of two qubits cannot be obtained, as the optimization problem for the
conditional entropy requires the solution to a pair of transcendental equations
in the state parameters. We apply our algorithm to run a numerical comparison
between quantum discord and an alternative, computable measure of non-classical
correlations, namely the geometric discord. We identify the extremally
non-classically correlated two--qubit states according to the (normalized)
geometric discord, at fixed value of the conventional quantum discord. The
latter cannot exceed the square root of the former for systems of two qubits.Comment: 8 pages, 2 figure
Non-geometric fluxes & tadpole conditions for exotic branes
We extend the -flux analysis carried out recently on the
type-II orientifold model to include
all the possible non-geometric fluxes. By deriving universal T-duality rules
for all the fluxes, we are able to write down a complete expression for the
superpotential for both the IIB and IIA theories. By exploiting the universal
T-duality rules that apply to all the branes in string theory, we then identify
all the exotic branes that can be consistently included to cancel the tadpoles
induced by the fluxes. Finally, we derive the representations of these branes
with respect to the duality symmetry of the model.Comment: 33 pages, refs. added. Notation improved. Discussion on the solutions
of the tadpole conditions added in the conclusions. Version published on JHE
The Impact of Government Spending on the Private Sector: Crowding-out versus Crowding-in Effects"
The aim of this paper is to analyze the impact of government spending on the private sector, assessing the existence of crowding-out versus crowding-in effects. Using a panel of 145 countries from 1960 to 2007, the results suggest that government spending produces important crowding-out effects, by negatively affecting both private consumption and investment. Moreover, while the effects do not seem to depend on the different phases of economic cycle, they vary considerably among regions. The results are economically and statiscally significant, and robust to several econometic techniques.Fiscal Policy, Government Spending, Crowding-out, Crowding-in.
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