Luttinger liquid superlattices: realization of gapless insulating phases

We investigate Luttinger Liquid superlattices, a periodic structure composed of two kinds of one-dimensional systems of interacting electrons. We calculate several properties of the low-energy sector: the effective charge and spin velocities, the compressibility, various correlation functions, the Landauer conductance and the Drude weight. The low-energy properties are subsumed into effective parameters, much like homogeneous one-dimensional systems. A generic result is the weighted average nature of these parameters, in proportion to the spatial extent of the underlying subunits, pointing to the possibility of ``engineered'' structures. As a specific realization, we consider a one-dimensional Hubbard superlattice, which consists of a periodic arrangement of two long Hubbard chains with different coupling constants and different hopping amplitudes. This system exhibits a rich phase diagram with several phases, both metallic and insulating. We have found that gapless insulating phases are present over a wide range of parameters.Comment: 16 pages, 15 figures, RevTeX

A Decade Lost and Found: Mexico and Chile in the 1980s

Chile and Mexico experienced severe economic crises in the early 1980s. This paper analyzes four possible explanations for why Chile recovered much faster than did Mexico. Comparing data from the two countries allows us to rule out a monetarist explanation, an explanation based on falls in real wages and real exchange rates, and a debt overhang explanation. Using growth accounting, a calibrated growth model, and economic theory, we conclude that the crucial difference between the two countries was the earlier policy reforms in Chile that generated faster productivity growth. The most crucial of these reforms were in banking and bankruptcy procedures.

A decade lost and found: Mexico and Chile in the 1980s

Chile and Mexico experienced severe economic crises in the early 1980s. This paper analyzes four possible explanations for why Chile recovered much faster than did Mexico. Comparing data from the two countries allows us to rule out a monetarist explanation, an explanation based on falls in real wages and real exchange rates, and a debt overhang explanation. Using growth accounting, a calibrated growth model, and economic theory, we conclude that the crucial difference between the two countries was the earlier policy reforms in Chile that generated faster productivity growth. The most crucial of these reforms were in banking and bankruptcy procedures.Depressions ; Productivity

Policy-Driven Productivity in Chile and Mexico in the 1980s and 1990s

Both Chile and Mexico experienced severe economic crises in the early 1980s, but Chile recovered much faster than did Mexico. Using growth accounting and a calibrated dynamic general equilibrium model, we conclude that the crucial determinant of this difference between the two countries was the faster productivity growth in Chile, rather than higher investment or employment. Our hypothesis is that this difference in productivity was driven by earlier policy reforms in Chile, the most crucial of which were in banking and bankruptcy procedures. We propose a theoretical framework in which government policy affects both the allocation of resources and the composition of firms.

Current status of las tablas de daimiel national park wetland and actions required for conservation

Wetlands are complex ecosystems that play multiple roles. ‘Las Tablas de Daimiel National Park’ (TDNP) undoubtedly plays a role in several ecosystem services and provides a connection between nature, farmers, scientists, residents, and other stakeholders. The state of degradation and/or vulnerability of this ecosystem (with a series of socio-economic implications) have led the publication of numerous articles. The work reported here provides a description of the growing importance of this wetland within the rural landscapes of La Mancha and emphasizes its state of degradation, mainly since pedological point of view. In this way, particular attention is required to assure the conservation of the Tablas of Daimiel Wetland; thus, several measures are proposed to improve the conservation of this area as to control and prohibit any dumping of any type of waste in the park or in its vicinityThis Research was funded by Organismo Autonomo Parques Nacionales (Autonomous Organism National Parks) of Spain (OAPN

Quantum confinement in Si and Ge nanostructures: Effect of crystallinity

We look at the relationship between the preparation method of Si and Ge nanostructures (NSs) and the structural, electronic, and optical properties in terms of quantum confinement (QC). QC in NSs causes a blue shift of the gap energy with decreasing NS dimension. Directly measuring the effect of QC is complicated by additional parameters, such as stress, interface and defect states. In addition, differences in NS preparation lead to differences in the relevant parameter set. A relatively simple model of QC, using a `particle-in-a-box'-type perturbation to the effective mass theory, was applied to Si and Ge quantum wells, wires and dots across a variety of preparation methods. The choice of the model was made in order to distinguish contributions that are solely due to the effects of QC, where the only varied experimental parameter was the crystallinity. It was found that the hole becomes de-localized in the case of amorphous materials, which leads to stronger confinement effects. The origin of this result was partly attributed to differences in the effective mass between the amorphous and crystalline NS as well as between the electron and hole. Corrections to our QC model take into account a position dependent effective mass. This term includes an inverse length scale dependent on the displacement from the origin. Thus, when the deBroglie wavelength or the Bohr radius of the carriers is on the order of the dimension of the NS the carriers `feel' the confinement potential altering their effective mass. Furthermore, it was found that certain interface states (Si-O-Si) act to pin the hole state, thus reducing the oscillator strength.Comment: arXiv admin note: substantial text overlap with arXiv:1111.201

MUSE observations of a changing-look AGN I: The re-appearance of the broad emission lines

Optical changing-look Active Galactic Nuclei (AGN) are a class of sources that change type within a short timescale of years or decades. This change is characterised by the appearance or disappearance of broad emission lines, often associated with dramatic AGN continuum flux changes that are orders of magnitude larger than those expected from typical AGN variability. In this work we study for the first time the host galaxy of a changing-look AGN, Mrk 590, using high spatial resolution optical and near-infrared observations. We discover that after ~ 10 yr absence, the optical broad emission lines of Mrk 590 have reappeared. The AGN optical continuum flux however, is still ~ 10 times lower than that observed during the most luminous state in the 1990s. The host galaxy shows a 4.5 kpc radius star-forming ring with knots of ionised and cold molecular gas emission. Extended ionised and warm molecular gas emission are detected in the nucleus, indicating that there is a reservoir of gas as close as 60 pc from the black hole. We observe a nuclear gas spiral between radii r ~ 0.5 - 2 kpc, which has been suggested as a dynamical mechanism able to drive the necessary gas to fuel AGN. We also discover blue-shifted and high velocity dispersion [O III] emission out to a radius of 1 kpc, tracing a nuclear gas outflow. The gas dynamics in Mrk 590 suggest a complex balance between gas inflow and outflow in the nucleus of the galaxy.Comment: Accepted for publication in MNRA

Plurality Voting: the statistical laws of democracy in Brazil

We explore the statistical laws behind the plurality voting system by investigating the election results for mayor held in Brazil in 2004. Our analysis indicate that the vote partition among mayor candidates of the same city tends to be "polarized" between two candidates, a phenomenon that can be closely described by means of a simple fragmentation model. Complex concepts like "government continuity" and "useful vote" can be identified and even statistically quantified through our approach.Comment: 4 pages, 4 figure