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

A prototypical model for tensional wrinkling in thin sheets

The buckling and wrinkling of thin films has recently seen a surge of interest among physicists, biologists, mathematicians and engineers. This has been triggered by the growing interest in developing technologies at ever decreasing scales and the resulting necessity to control the mechanics of tiny structures, as well as by the realization that morphogenetic processes, such as the tissue-shaping instabilities occurring in animal epithelia or plant leaves, often emerge from mechanical instabilities of cell sheets. While the most basic buckling instability of uniaxially compressed plates was understood by Euler more than 200 years ago, recent experiments on nanometrically thin (ultrathin) films have shown significant deviations from predictions of standard buckling theory. Motivated by this puzzle, we introduce here a theoretical model that allows for a systematic analysis of wrinkling in sheets far from their instability threshold. We focus on the simplest extension of Euler buckling that exhibits wrinkles of finite length - a sheet under axisymmetric tensile loads. This geometry, whose first study is attributed to Lam´e, allows us to construct\ud a phase diagram that demonstrates the dramatic variation of wrinkling patterns from near-threshold to far-from-threshold conditions. Theoretical arguments and comparison to experiments show that for thin sheets the far-from-threshold regime is expected to emerge under extremely small compressive loads, emphasizing the relevance of our analysis for nanomechanics applications

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

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

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