Tax Systems and tax reforms in Latin America, Part I : country studies, Colombia

This paper is a part of a wider research concerning taxation in the main world economic areas, carried on at the Department of Public economic on the University of Pvia, Italy, directed by L. Bernardi and P. Profeta, under the supervision of Vito Tanzi. The paper illustrates and discusses the Colombian tax ssystems with respect to its structure, developments and reforms until the last chenges of 2007, December.Tax Systems Tax Reforms Colombia

Bounds on the tensor rank

We give a sufficient criterion for a lower bound of the cactus rank of a tensor. Then we refine that criterion in order to be able to give an explicit sufficient condition for a non-redundant decomposition of a tensor to be minimal and unique.Comment: 14 page

Selection bias in the M_BH-sigma and M_BH-L correlations and its consequences

It is common to estimate black hole abundances by using a measured correlation between black hole mass and another more easily measured observable such as the velocity dispersion or luminosity of the surrounding bulge. The correlation is used to transform the distribution of the observable into an estimate of the distribution of black hole masses. However, different observables provide different estimates: the Mbh-sigma relation predicts fewer massive black holes than does the Mbh-L relation. This is because the sigma-L relation in black hole samples currently available is inconsistent with that in the SDSS sample, from which the distributions of L or sigma are based: the black hole samples have smaller L for a given sigma or have larger sigma for a given L. This is true whether L is estimated in the optical or in the NIR. If this is a selection rather than physical effect, then the Mbh-sigma and Mbh-L relations currently in the literature are also biased from their true values. We provide a framework for describing the effect of this bias. We then combine it with a model of the bias to make an estimate of the true intrinsic relations. While we do not claim to have understood the source of the bias, our simple model is able to reproduce the observed trends. If we have correctly modeled the selection effect, then our analysis suggests that the bias in the relation is likely to be small, whereas the relation is biased towards predicting more massive black holes for a given luminosity. In addition, it is likely that the Mbh-L relation is entirely a consequence of more fundamental relations between Mbh and sigma, and between sigma and L. The intrinsic relation we find suggests that at fixed luminosity, older galaxies tend to host more massive black holes.Comment: 12 pages, 7 figures. Accepted by ApJ. We have added a figure showing that a similar bias is also seen in the K-band. A new appendix describes the BH samples as well as the fits used in the main tex

A nonlinear procedure for the analysis of RC beams

Abstract This work deals with the development of a computational method for the nonlinear analysis of reinforced concrete beams subjected to general loading and constraint conditions, able to catch crack formation and propagation. To this aim, a layered beam finite element is developed. The displacement field along beam axis and height is modelled through polynomial functions, whose number of terms is varied based on the complexity of the considered problem. The mechanical nonlinearity of the material is taken into account by implementing a smeared constitutive model for cracked reinforced concrete elements. The effectiveness of the proposed procedure, which can be applied to the analysis of both new and existing buildings, is proved through comparison with significant experimental data from technical literature, relative to both statically determinate and indeterminate beams

Transverse reinforcement optimization of a precast special roof element through an experimental and numerical procedure

The transverse behavior of a long span three-plate precast roof element is investigated by means of an experimental and numerical research. The performed study highlights that the failure mode of this folded-plate element is strongly influenced by the amount of transverse reinforcement in the wings. This latter is usually designed through simplified methods, which often lead to over-dimensioning in terms of steel welded mesh. To avoid excessive costs for the producers, transverse reinforcement optimization should be required. In this work, a non-linear FE modelling was applied for this purpose. The reliability of the followed numerical procedure was first verified by an initial type testing (i.e. experimental load test up to failure). The agreement between numerical and experimental results showed the efficiency of the model in simulating all the main sources of non-linearity related to both material behavior and element geometry. Numerical analyses were so used to perform a parametric study as a function of transverse reinforcement amount, aimed at determining a coefficient of “model inaccuracy”. This coefficient should be used as a correction factor for the element design in routine calculations based on beam theory

Stability of a convex feasibility problem

The 2-sets convex feasibility problem aims at finding a point in the intersection of two closed convex sets $A$ and $B$ in a normed space $X$. More generally, we can consider the problem of finding (if possible) two points in $A$ and $B$, respectively, which minimize the distance between the sets. In the present paper, we study some stability properties for the convex feasibility problem: we consider two sequences of sets, each of them converging, with respect to a suitable notion of set convergence, respectively, to $A$ and $B$. Under appropriate assumptions on the original problem, we ensure that the solutions of the perturbed problems converge to a solution of the original problem. We consider both the finite-dimensional and the infinite-dimensional case. Moreover, we provide several examples that point out the role of our assumptions in the obtained results.Comment: 17 page

EVALUATION OF CRACK WIDTH IN RC TIES THROUGH A NUMERICAL "RANGE" MODEL

The problem of cracking in reinforced concrete (RC) tensile members has been studied extensively in the past, not only for the analysis of tension zones, but also for understanding and modeling the behavior of beams in bending. Despite the large number of published studies, there is still no agreement on the relative importance of the most critical parameters influencing crack width and spacing (especially bond-slip and stress diffusion in concrete cover), as proved by the development of more than twenty different formulae available in technical literature [1]. Aim of this work is to investigate if a model based exclusively on bond-slip is able to predict correctly crack width and spacing or if the contribution of stress diffusion in concrete cover - which is included in several design Codes and in some numerical or analytical approaches – must be considered. To this purpose, a one-dimensional numerical model based on bond between steel and concrete is here developed for analyzing the behavior of RC tension ties, by also taking into account the influence of bond deterioration near crack surfaces. To consider the uncertainty of crack pattern evolution, the model provides a range of crack widths and spacing that, according to bond theory, are possible for a given load. The effectiveness of the proposed procedure is verified through comparisons with significant experimental results on RC tension members available in the technical literature [2-3], both in terms of global behavior and in terms of crack width and crack spacing evolution as loading increases. These comparisons prove that bond deterioration improves the results and that the proposed approach can be successfully adopted for design purposes, since it provides a correct estimate of maximum crack width. The obtained results are also compared with Codes provisions and the effectiveness of different approaches for predicting crack width is analyzed and discussed. References [1] Borosnyoi A, Balazs GL. Models for flexural cracking in concrete: the state of the art. Struct Concr, 2005; 6(2): 53-62. [2] Wu HQ, Gilbert RI. An experimental study of tension stiffening in reinforced concrete members under short-term and long-term loads. In: UNICIV Report No. R-449, 2008, The University of New South Wales, Sidney, Australia. [3] Gijsbers FBJ, Hehemann AA. Enige trekproven op gewapend beton (Some tensile tests on reinforced concrete). In: Report BI-77-61, 1977, TNO Inst for Building Mat and Struct, Delft, The Netherlands

Vulnerability assessment of Italian Rationalist architecture: two case studies

The work is focused on the structural vulnerability assessment of two historical constructions, chosen as case-studies representative of a recurrent typology of Italian rationalist architecture, dating back to the Fascist period, often hosting public offices. Both examined buildings have similar dimensions and geometry, being characterised by five/six storeys and by an almost square plan with an inner courtyard, and are located in EmiliaRomagna, in zones of medium seismic hazard. The older building, dating back to the Thirties and located in Ravenna, has a mixed masonry-reinforced concrete structure, while the other one, built in the late forties and located in Parma, is characterised by an unreinforced masonry structure with some limited reinforced concrete elements. For the vulnerability assessment of the two buildings, a multi-disciplinary approach was followed, including the historical documents search concerning both the investigated buildings and the surrounding areas, the detailed geometrical and structural survey, the identification of materials, and in situ and laboratory tests to evaluate materials mechanical properties. These activities allowed reaching an adequate level of knowledge about the present conditions of the structures and their critical deficiencies. This knowledge path is not only necessary for the subsequent numerical analyses, but is also important as it allows targeting the repairing interventions, possibly reducing their final costs, in agreement with the “minimum intervention” approach for heritage buildings

ASSESSMENT OF INDOOR POLLUTION IN A SCHOOL ENVIRONMENT THROUGH BOTH PASSIVE AND CONTINUOUS SAMPLINGS

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fracture toughness of fibre reinforced concrete determined by means of numerical analysis

Abstract As is well-known, the addition of fibres to concrete mix (Fibre Reinforced Concrete, FRC) produces a positive effect on cracking behaviour. In this work, the results of an experimental campaign on FRC specimens with randomly distributed micro-synthetic polypropylene fibrillated fibres are examined. The tests concern single-notched beams under three-point bending, where the fibre content varies. Such an experimental testing is numerically analysed through a non-linear finite element model, named 2D-PARC, where a proper constitutive law for fibre-reinforced concrete is implemented. The load-crack mouth opening displacement (CMOD) curves numerically obtained are employed to determine the critical stress-intensity factor (fracture toughness) for different values of fibre content, according to the two-parameter model. The comparison between such numerical results and those obtained by applying the two-parameter model to the experimental load-CMOD curves is performed