On Recycling and Technological Externalities

recycling;natural resources;production set;externalities

Landfill Construction and Capacity Expansion

We study the optimal capacity and lifetime of landfills taking into account their sequential nature.Such an optimal capacity is characterized by the so-called Optimal Capacity Condition.Particular versions of this condition are obtained for two alternative settings: first, if all the landfills are to have the same capacity, and second, if each of them is allowed to have a different capacity.In the second case we obtain an Optimal Control problem, with mixed elements of both continuous and discrete time.The resulting optimization problems involve dividing a time horizon of planning into several subintervals of endogenously decided length.The results obtained may be useful to address other economic problems such as private and public investments, consumption decisions on durable goods, etc.investements;resources;capacity;costs

Magneto-elastic oscillations of neutron stars: exploring different magnetic field configurations

We study magneto-elastic oscillations of highly magnetized neutron stars (magnetars) which have been proposed as an explanation for the quasi-periodic oscillations (QPOs) appearing in the decaying tail of the giant flares of soft gamma-ray repeaters (SGRs). We extend previous studies by investigating various magnetic field configurations, computing the Alfv\'en spectrum in each case and performing magneto-elastic simulations for a selected number of models. By identifying the observed frequencies of 28 Hz (SGR 1900+14) and 30 Hz (SGR 1806-20) with the fundamental Alfv\'en QPOs, we estimate the required surface magnetic field strength. For the magnetic field configurations investigated (dipole-like poloidal, mixed toroidal-poloidal with a dipole-like poloidal component and a toroidal field confined to the region of field lines closing inside the star, and for poloidal fields with an additional quadrupole-like component) the estimated dipole spin-down magnetic fields are between 8x10^14 G and 4x10^15 G, in broad agreement with spin-down estimates for the SGR sources producing giant flares. A number of these models exhibit a rich Alfv\'en continuum revealing new turning points which can produce QPOs. This allows one to explain most of the observed QPO frequencies as associated with magneto-elastic QPOs. In particular, we construct a possible configuration with two turning points in the spectrum which can explain all observed QPOs of SGR 1900+14. Finally, we find that magnetic field configurations which are entirely confined in the crust (if the core is assumed to be a type I superconductor) are not favoured, due to difficulties in explaining the lowest observed QPO frequencies (f<30 Hz).Comment: 21 pages, 16 figures, 6 tables, matched to version accepted by MNRAS with extended comparison/discussion to previous wor

Análisis morfométrico de vértebra c2 evaluada en telerradiografías de perfil de un centro privado referencial de radiología maxilofacial de la región del Maule.

59 p.INTRODUCCIÓN: Las patologías de la articulación atlanto-axial han sido un tópico de interés general en la investigación científica, debido al alto riesgo de lesiones neurológicas, subluxación o inestabilidad atlanto-axial. Por esto es importante estudiar las características morfométricas de la vértebra cervical axis en telerradiografía de perfil debido al alto predominio de patologías relacionadas con la inestabilidad atlanto-axial y el poco conocimiento de la morfometría de esta vértebra. OBJETIVO GENERAL: Determinar las características morfométricas de Axis en telerradiografía de perfil de pacientes de un Centro de Referencia de Radiología Maxilofacial de la región del Maule, tanto en el plano vertical como en el plano sagital. MATERIALES Y MÉTODOS: Estudio observacional descriptivo de corte transversal cuya muestra fue de 378 telerradiografías de perfil obtenidas de un Centro de Referencia de Radiología Maxilofacial de la Región del Maule. Se utilizó el software SIDEXIS para analizar: distancia OC (altura proceso odontoides), distancia CB (altura de cuerpo vertebral), distancia OB (longitud vértice proceso odontoides- base del cuerpo vertebral), distancia EP (longitud lineal de arco más proceso espinoso), distancia EI (longitud proceso espinoso), distancia IS (longitud lineal de faceta articular), distancia PA (longitud anteroposterior del cuerpo vertebral) y distancia EA (longitud vertebral total antero-posterior). Las imágenes fueron observadas por dos operadores al mismo tiempo. RESULTADOS: El 68% de la muestra correspondió a sexo femenino y 32% a masculino. Las edades fluctuaron de 16 a 40 años, promedio de 23,15 años. Se obtuvieron promedios con diferencias estadísticamente significativas entre hombres y mujeres en todas las distancias excepto en distancia IS (faceta articular inferior). CONCLUSIONES: Existen diferencias estadísticamente significativas en los promedios de las medidas de población femenina y masculina, las que se correlacionan con estudios anteriores. Se sugiere continuar con estudios con mayor población para establecer características morfométricas de axis como herramienta para determinar dimorfismo sexual. PALABRAS CLAVES: Morfometría, vértebra axis, dimorfismo sexual, telerradiografía de perfil

Capillary deformations of bendable films

We address the partial wetting of liquid drops on ultrathin solid sheets resting on a deformable foundation. Considering the membrane limit of sheets that can relax compression through wrinkling at negligible energetic cost, we revisit the classical theory for the contact of liquid drops on solids. Our calculations and experiments show that the liquid-solid-vapor contact angle is modified from the Young angle, even though the elastic bulk modulus (E) of the sheet is so large that the ratio between the surface tension γ and E is of molecular size. This finding establishes a new type of “soft capillarity” that stems from the bendability of thin elastic bodies rather than from material softness. We also show that the size of the wrinkle pattern that emerges in the sheet is fully predictable, thus resolving a puzzle noticed in several previous attempts to model “drop-on-a-floating-sheet” experiments, and enabling a reliable usage of this setup for the metrology of ultrathin films

Anomalous strength of membranes with elastic ridges

We report on a simulational study of the compression and buckling of elastic ridges formed by joining the boundary of a flat sheet to itself. Such ridges store energy anomalously: their resting energy scales as the linear size of the sheet to the 1/3 power. We find that the energy required to buckle such a ridge is a fixed multiple of the resting energy. Thus thin sheets with elastic ridges such as crumpled sheets are qualitatively stronger than smoothly bent sheets.Comment: 4 pages, REVTEX, 3 figure

Genes involved in carotene synthesis and mating in Blakeslea trispora

Mating of Blakeslea trispora and other molds of the order Mucorales requires the interaction of mycelia of opposite sex, (+) and (-), leading to the development of specialized structures and to an enhanced accumulation of beta-carotene. Industry obtains beta-carotene by co-cultivating appropriate strains of Blakeslea (mated cultures). Gene transcription in single and mated cultures was assayed by cDNA-AFLP, a technique to observe the differential expression of subsets of mRNA fragments. Overexpression in mated cultures is about ten times more frequent than underexpression. We obtained and sequenced fragments of 97 candidate genes that appeared to be overexpressed during mating and confirmed four of them by reverse transcription and real-time PCR. Comparisons with gene sequences from other organisms suggest functions in carotene biosynthesis (4 genes), energy metabolism (8), cell wall synthesis (1), transfer of acetyl groups (1), and regulatory processes (10). Sodium acetate inhibited sexual overexpression in about two-thirds of the candidate genes and acted as a signal with broad effects on the metabolism and the morphology of mated cultures. Our work offers new materials for the study of carotene biosynthesis and its regulation and for the improvement of carotene production with Mucorales

A Nexafs Study of Nitric Oxide Layers Adsorbed from a nitrite Solution onto a Pt(111) Surface

NO molecules adsorbed on a Pt(111) surface from dipping in an acidic nitrite solution are studied by near edge X-ray absorption fine structure spectroscopy (NEXAFS), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) techniques. LEED patterns and STM images show that no long range ordered structures are formed after NO adsorption on a Pt(111) surface. Although the total NO coverage is very low, spectroscopic features in N K-edge and O K-edge absorption spectra have been singled out and related to the different species induced by this preparation method. From these measurements it is concluded that the NO molecule is adsorbed trough the N atom in an upright conformation. The maximum saturation coverage is about 0.3 monolayers, and although nitric oxide is the major component, nitrite and nitrogen species are slightly co-adsorbed on the surface. The results obtained from this study are compared with those previously reported in the literature for NO adsorbed on Pt(111) under UHV conditions

Strain-induced Evolution of Electronic Band Structures in a Twisted Graphene Bilayer

Here we study the evolution of local electronic properties of a twisted graphene bilayer induced by a strain and a high curvature. The strain and curvature strongly affect the local band structures of the twisted graphene bilayer; the energy difference of the two low-energy van Hove singularities decreases with increasing the lattice deformations and the states condensed into well-defined pseudo-Landau levels, which mimic the quantization of massive Dirac fermions in a magnetic field of about 100 T, along a graphene wrinkle. The joint effect of strain and out-of-plane distortion in the graphene wrinkle also results in a valley polarization with a significant gap, i.e., the eight-fold degenerate Landau level at the charge neutrality point is splitted into two four-fold degenerate quartets polarized on each layer. These results suggest that strained graphene bilayer could be an ideal platform to realize the high-temperature zero-field quantum valley Hall effect.Comment: 4 figure