Urban Structure and Growth

Most economic activity occurs in cities. This creates a tension between local increasing returns, implied by the existence of cities, and aggregate constant returns, implied by balanced growth. To address this tension, we develop a theory of economic growth in an urban environment. We show that the urban structure is the margin that eliminates local increasing returns to yield constant returns to scale in the aggregate, which is sufficient to deliver balanced growth. In a multi-sector economy with specific factors and productivity shocks, the same mechanism leads to a city size distribution that is well described by a power distribution with coefficient one: Zipf's Law. Under certain assumptions our theory produces Zipf's Law exactly. More generally, it produces the systematic deviations from Zipf's Law observed in the data, including the under-representation of small cities and the absence of very large ones. In general, the model identifies the standard deviation of industry productivity shocks as the key parameter determining dispersion in the city size distribution. We present evidence that the relationship between the dispersion of city sizes and the variance of productivity shocks is consistent with the data.

Firm Size Dynamics in the Aggregate Economy

Why do firm growth and exit rates decline with size? What determines the size distribution of firms? This paper presents a theory of firm dynamics that simultaneously rationalizes the basic facts on firm growth, exit, and size distributions. The theory emphasizes the accumulation of industry specific human capital in response to industry specific productivity shocks. The theory implies that firm growth and exit rates should decline faster with size, and the size distribution should have thinner tails, in sectors that use human capital less intensively, or correspondingly, physical capital more intensively. In line with the theory, we document substantial sectoral heterogeneity in US firm dynamics and firm size distributions, which is well explained by variation in physical capital intensities.

Urban structure and growth

Most economic activity occurs in cities. This creates a tension between local increasing returns, implied by the existence of cities, and aggregate constant returns, implied by balanced growth. To address this tension, we develop a theory of economic growth in an urban environment. We show how the urban structure is the margin that eliminates local increasing returns to yield constant returns to scale in the aggregate, thereby implying a city size distribution that is well described by a power distribution with coefficient one: Zipf's Law. Under strong assumptions our theory produces Zipf's Law exactly. More generally, it produces the systematic deviations from Zipf's Law observed in the data, namely, the underrepresentation of small cities and the absence of very large ones. In these cases, the model identifies the standard deviation of industry productivity shocks as the key element determining dispersion in the city size distribution. We present evidence that the dispersion of city sizes is consistent with the dispersion of productivity shocks in the data.

A physics-based life prediction methodology for thermal barrier coating systems

A novel mechanistic approach is proposed for the prediction of the life of thermal barrier coating (TBC) systems. The life prediction methodology is based on a criterion linked directly to the dominant failure mechanism. It relies on a statistical treatment of the TBC's morphological characteristics, non-destructive stress measurements and on a continuum mechanics framework to quantify the stresses that promote the nucleation and growth of microcracks within the TBC. The last of these accounts for the effects of TBC constituents' elasto-visco-plastic properties, the stiffening of the ceramic due to sintering and the oxidation at the interface between the thermally insulating yttria stabilized zirconia (YSZ) layer and the metallic bond coat. The mechanistic approach is used to investigate the effects on TBC life of the properties and morphology of the top YSZ coating, metallic low-pressure plasma sprayed bond coat and the thermally grown oxide. Its calibration is based on TBC damage inferred from non-destructive fluorescence measurements using piezo-spectroscopy and on the numerically predicted local TBC stresses responsible for the initiation of such damage. The potential applicability of the methodology to other types of TBC coatings and thermal loading conditions is also discussed

Froude number scaling unifies impact trajectories into granular media across gravitational conditions

The interactions of solid objects with granular media is countered by a resistance force that stems from frictional forces between the grains and the media's resistance to inertia imposed by the intruder. Earlier theories of granular intrusion have suggested an additive contribution of these two families of forces and had tremendous success in predicting resistive forces on arbitrary shaped objects. However, it remains unclear how these forces are influenced by gravitational conditions. We examine the role of gravity on surface impact behavior into cohesionless granular media using hundreds of soft-sphere discrete element simulations, we demonstrate that the outcome of impacts remain qualitatively similar under varying gravitational conditions if initial velocities are scaled with the Froude number, suggesting an underlying law. Using theoretical arguments, we provide reasoning for the observed universality and show that there is a hidden dependency in resistive forces into granular media on Froude number. Following the theoretical framework, we show that Froude number scaling precisely collapses impact trajectories across gravitational conditions, setting the foundation for explorations in granular behavior beyond Earth

Development of mental health first aid guidelines for problem drinking: a Delphi expert consensus study in Argentina and Chile

BACKGROUND: Among all psychoactive substances, alcohol consumption presents the most significant public health problem and is a leading risk factor for overall disease burden in Latin America. However, most people who meet criteria for a substance use disorder do not receive treatment in primary or secondary care sources. Community members can play a role in helping people to seek help as they are likely to encounter people experiencing problem drinking and recognize the signs. However, many do not have adequate mental health first aid knowledge or skills to provide help. We aimed to culturally adapt the existing English-language mental health first aid guidelines for helping someone with problem drinking for Argentina and Chile. METHODS: The Delphi consensus method was used to determine the importance of helping actions translated from the English-language guidelines and to add new actions suggested by expert panellists. The importance of each statement was rated by two expert panels. Panel one included people with lived experience (either their own or as a support person, n = 23) recruited in Argentina and panel two included health professionals (n = 31) recruited in Argentina and Chile. RESULTS: Overall, 165 helping actions were endorsed by panellists across two consecutive survey rounds. Endorsed items included 132 of the 182 items translated into Spanish from the English-language guidelines and 33 of the 61 new items generated from panellists' comments in the first survey round. CONCLUSIONS: While there were some similarities in recommended helping actions between English-speaking countries, and Argentina and Chile, key differences were seen in attitudes to low-risk drinking. While there was a relatively high level of agreement between health professionals and people with lived experience, some divergence of opinion was seen, particularly in the area of commitment to recovery as a condition for help. Future research should explore the implementation of the guidelines

Análisis arqueométrico de pigmentos del sitio arqueológico Tambo Colorado por difracción de rayos X sincrotrón

A pesar de la excepcional arquitectura y policromía del sitio arqueológico de Tambo Colorado, no ha habidotrabajos de conservación ni en las estructuras arquitectónicas de tierra cruda, ni en las superficies. Estos trabajosrequieren una comprensión adecuada del estado de conservación de la arquitectura del sitio y el análisisde los materiales utilizados. Con este propósito, los resultados del presente estudio pretenden explicar la naturalezade los materiales (pigmentos) utilizados en las pinturas murales, así como determinar las fuentes deestos materiales (canteras). Para ello, pigmentos de cantera fueron investigados por la técnica de difracciónde rayos X, usando radiación sincrotrón, y refinamiento estructural por el método de Rietveld. Se determinóla composición de los pigmentos, identificando las fases de anortita, hematita, cuarzo, clorita, halita, yeso,ortoclasa, illita, jarosita, calcita, caolinita, zinwaldita, cristobalita, anhidrita y albita. El refinamiento Rietveldconfirmó la presencia de estas fases y determinó el porcentaje en peso de cada una de ellas.Palabras-llave: Pigmento, difracción de rayos-X, método de Rietveld, radiación sincrotrón