424 research outputs found
Estimating the underground economy by using MIMIC models: A response to T. BreuschÂŽs critique
Breusch (2005b) critically addresses an important and challenging question: Is it reliable to use the Multiple Indicators Multiple Causes model to estimate Shadow Economy? Breusch concludes that this approach is not suitable for the purpose. Breuschâs paper highlights the different procedures and hypotheses about the estimation of the size and development of the shadow economy in three papers: Giles and Tedds (2002a), DellâAnno and Schneider (2003) and Bajada and Schneider (2005). In this paper, we will react and provide some answers to Breuschâs criticisms with special reference to the criticisms of the DellâAnno and Schneider (2003) paper. According with us, the MIMIC model is still one of the best approaches to this purpose.shadow economy; MIMIC model; structural modelling.
Realistic continuous-variable quantum teleportation with non-Gaussian resources
We present a comprehensive investigation of nonideal continuous-variable
quantum teleportation implemented with entangled non-Gaussian resources. We
discuss in a unified framework the main decoherence mechanisms, including
imperfect Bell measurements and propagation of optical fields in lossy fibers,
applying the formalism of the characteristic function. By exploiting
appropriate displacement strategies, we compute analytically the success
probability of teleportation for input coherent states, and two classes of
non-Gaussian entangled resources: Two-mode squeezed Bell-like states (that
include as particular cases photon-added and photon-subtracted de-Gaussified
states), and two-mode squeezed cat-like states. We discuss the optimization
procedure on the free parameters of the non-Gaussian resources at fixed values
of the squeezing and of the experimental quantities determining the
inefficiencies of the non-ideal protocol. It is found that non-Gaussian
resources enhance significantly the efficiency of teleportation and are more
robust against decoherence than the corresponding Gaussian ones. Partial
information on the alphabet of input states allows further significant
improvement in the performance of the non-ideal teleportation protocol.Comment: 14 pages, 6 figure
Continuous variable quantum teleportation with non-Gaussian resources
We investigate continuous variable quantum teleportation using non-Gaussian
states of the radiation field as entangled resources. We compare the
performance of different classes of degaussified resources, including two-mode
photon-added and two-mode photon-subtracted squeezed states. We then introduce
a class of two-mode squeezed Bell-like states with one-parameter dependence for
optimization. These states interpolate between and include as subcases
different classes of degaussified resources. We show that optimized squeezed
Bell-like resources yield a remarkable improvement in the fidelity of
teleportation both for coherent and nonclassical input states. The
investigation reveals that the optimal non-Gaussian resources for continuous
variable teleportation are those that most closely realize the simultaneous
maximization of the content of entanglement, the degree of affinity with the
two-mode squeezed vacuum and the, suitably measured, amount of non-Gaussianity.Comment: 12 pages, 12 figure
Structure of multiphoton quantum optics. II. Bipartite systems, physical processes, and heterodyne squeezed states
Extending the scheme developed for a single mode of the electromagnetic field
in the preceding paper ``Structure of multiphoton quantum optics. I. Canonical
formalism and homodyne squeezed states'', we introduce two-mode nonlinear
canonical transformations depending on two heterodyne mixing angles. They are
defined in terms of hermitian nonlinear functions that realize heterodyne
superpositions of conjugate quadratures of bipartite systems. The canonical
transformations diagonalize a class of Hamiltonians describing non degenerate
and degenerate multiphoton processes. We determine the coherent states
associated to the canonical transformations, which generalize the non
degenerate two--photon squeezed states. Such heterodyne multiphoton squeezed
are defined as the simultaneous eigenstates of the transformed, coupled
annihilation operators. They are generated by nonlinear unitary evolutions
acting on two-mode squeezed states. They are non Gaussian, highly non
classical, entangled states. For a quadratic nonlinearity the heterodyne
multiphoton squeezed states define two--mode cubic phase states. The
statistical properties of these states can be widely adjusted by tuning the
heterodyne mixing angles, the phases of the nonlinear couplings, as well as the
strength of the nonlinearity. For quadratic nonlinearity, we study the
higher-order contributions to the susceptibility in nonlinear media and we
suggest possible experimental realizations of multiphoton conversion processes
generating the cubic-phase heterodyne squeezed states.Comment: 16 pages, 23 figure
Optimization of the transmission of observable expectation values and observable statistics in Continuous Variable Teleportation
We analyze the statistics of observables in continuous variable quantum
teleportation in the formalism of the characteristic function. We derive
expressions for average values of output state observables in particular
cumulants which are additive in terms of the input state and the resource of
teleportation. Working with Squeezed Bell-like states, which may be optimized
in a free parameter for better teleportation performance we discuss the
relation between resources optimal for fidelity and for different observable
averages. We obtain the values of the free parameter which optimize the central
momenta and cumulants up to fourth order. For the cumulants the distortion
between in and out states due to teleportation depends only on the resource. We
obtain optimal parameters for the second and fourth order cumulants which do
not depend on the squeezing of the resource. The second order central momenta
which is equal to the second order cumulants and the photon number average are
optimized by the same resource. We show that the optimal fidelity resource,
found in reference (Phys. Rev. A {\bf 76}, 022301 (2007)) to depend also on the
characteristics of input, tends for high squeezing to the resource which
optimizes the second order momenta. A similar behavior is obtained for the
resource which optimizes the photon statistics which is treated here using the
sum of the squared differences in photon probabilities of input and output
states as the distortion measure. This is interpreted to mean that the
distortions associated to second order momenta dominates the behavior of the
output state for large squeezing of the resource. Optimal fidelity and optimal
photon statistics resources are compared and is shown that for mixtures of Fock
states they are equivalent.Comment: 25 pages, 11 figure
Informality, Inequality and ICT in Transition economies
In this paper, we examine the role of the quality of institutional infrastructure and information and communication technology (ICT) in the relationship between the size of the informal sector (IS) and income inequality. Following our results, the sign of the relationship between IS and income inequality depends on the quality of institutions. When institutions are weak, agents invest less human capital and ICT in the formal sector (FS), thereby reducing income inequality. Utilizing panel data for sixteen transition countries we show that the relationship between the size of the IS and the level of income inequality is ambiguous. Our findings highlight the problem of measuring the relative size of the IS which is a hidden entity. We control for robustness of our findings using alternative proxies of ICT, human capital, and institutional quality and some interaction terms among these variables
Optimal estimation of losses at the ultimate quantum limit with non-Gaussian states
We address the estimation of the loss parameter of a bosonic channel probed
by arbitrary signals. Unlike the optimal Gaussian probes, which can attain the
ultimate bound on precision asymptotically either for very small or very large
losses, we prove that Fock states at any fixed photon number saturate the bound
unconditionally for any value of the loss. In the relevant regime of low-energy
probes, we demonstrate that superpositions of the first low-lying Fock states
yield an absolute improvement over any Gaussian probe. Such few-photon states
can be recast quite generally as truncations of de-Gaussified photon-subtracted
states.Comment: 4 pages, 3 figure
Diversity and spatial distribution of metalreducing bacterial assemblages in groundwaters of different redox conditions
The spatial distribution and diversity of metal-reducing bacterial assemblages belonging to Geobacteraceae were studied in groundwaters with different physicochemical characteristics by means of terminal-restriction fragment length polymorphism (T-RFLP) molecular fingerprinting, as applied to the 16S rRNA gene. The physicochemical conditions of these environments were unfavorable to support active-metal-reducing processes. The highest diversity of Geobacteraceae was observed in groundwater samples characterized by the highest dissolved Fe and Mn concentrations. T-RFLP analyses revealed major differences in the Geobacteraceae ribotype diversity and community composition of the groundwater samples as well as a considerable variability and spatial turnover of Geobacteraceae assemblages. Results from this work suggest that changes in the physicochemical characteristics of the aquifer deeply influence the richness and community structure of Geobacteraceae, even in those systems in which metal-reduction processes are not dominant. [Int Microbiol 2009; 12(3):153-159
Hierarchies of Geometric Entanglement
We introduce a class of generalized geometric measures of entanglement. For
pure quantum states of elementary subsystems, they are defined as the
distances from the sets of -separable states (). The entire set
of generalized geometric measures provides a quantification and hierarchical
ordering of the different bipartite and multipartite components of the global
geometric entanglement, and allows to discriminate among the different
contributions. The extended measures are applied to the study of entanglement
in different classes of -qubit pure states. These classes include and
states, and their symmetric superpositions; symmetric multi-magnon
states; cluster states; and, finally, asymmetric generalized -like
superposition states. We discuss in detail a general method for the explicit
evaluation of the multipartite components of geometric entanglement, and we
show that the entire set of geometric measures establishes an ordering among
the different types of bipartite and multipartite entanglement. In particular,
it determines a consistent hierarchy between and states, clarifying
the original result of Wei and Goldbart that states possess a larger global
entanglement than states. Furthermore, we show that all multipartite
components of geometric entanglement in symmetric states obey a property of
self-similarity and scale invariance with the total number of qubits and the
number of qubits per party.Comment: 16 pages, 7 figures. Final version, to appear in Phys. Rev.
An ARDL model of unrecorded and recorded economies in Turkey
Purpose: The goal of this paper is twofold: to estimate the unrecorded economy (UE) of Turkey over the period 1987-2007 using a revised version of the currency demand approach and to analyze the relationship between UE and recorded GDP.
Design/methodology/approach: we propose to measure UE by the autoregressive distributed lag (ARDL) approach to cointegration analysis. Toda- Yamamoto causality tests are also conducted to identify the relationship between unrecorded and recorded GDP.
Findings: This research provides fresh evidence on the size of the UE to the recorded GDP in Turkey which ranges from 10.7% to 18.9% over the estimation period. Moreover, empirical evidence concretely suggests that causality runs from the recorded GDP to the UE. However, there exists a mild reverse causality.
Research limitations/implications: Measures of the UE, and particularly those based on monetary approaches, have been criticized on several accounts, including their lack of robustness and weak theoretical foundations (e.g. the velocity of money in the recorded economy and in the UE is the same).
Practical implications: The analysis suggests that the UE is pro-cyclical with respect to the recorded GDP. It suggests that the phenomenon of UE is more dangerous when the economy is in expensive phase. Hence, during a positive business cycle it is clearly desirable for government the anti-UE controls should be more effective.
Originality/value: The ARDL approach to estimating the size of UE eliminates criticism that the previous currency demand estimations are based on partial adjustment models. Therefore, our econometric selected cointegration methodology and causality test is an improvement over the existing studies
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