The great diversification and its undoing

We investigate the hypothesis that macroeconomic fluctuations are primitively the results of many microeconomic shocks, and show that it has significant explanatory power for the evolution of macroeconomic volatility. We define “fundamental” volatility as the volatility that would arise from an economy made entirely of idiosyncratic microeconomic shocks, occurring primitively at the level of sectors or firms. In its empirical construction, motivated by a simple model, the sales share of different sectors vary over time (in a way we directly measure), while the volatility of those sectors remains constant. We find that fundamental volatility accounts for the swings in macroeconomic volatility in the US and the other major world economies in the past half century. It accounts for the “great moderation” and its undoing. Controlling for our measure of fundamental volatility, there is no break in output volatility. The initial great moderation is due to a decreasing share of manufacturing between 1975 and 1985. The recent rise of macroeconomic volatility is due to the increase of the size of the financial sector. We provide a model to think quantitatively about the large comovement generated by idiosyncratic shocks. As the origin of aggregate shocks can be traced to identifiable microeconomic shocks, we may better understand the origins of aggregate fluctuations.

Understanding bubbly episodes

bubbles, dynamic inefficiency, economic growth, financial frictions, pyramid schemes

Aggregate fluctuations and the network structure of intersectoral trade

This paper analyzes the flow of intermediate inputs across sectors by adopting a network perspective on sectoral interactions. I apply these tools to show how fluctuations in aggregate economic activity can be obtained from independent shocks to individual sectors. First, I characterize the network structure of input trade in the U.S. On the demand side, a typical sector relies on a small number of key inputs and sectors are homogeneous in this respect. However, in their role as input-suppliers sectors do differ: many specialized input suppliers coexist alongside general purpose sectors functioning as hubs to the economy. I then develop a model of intersectoral linkages that can reproduce these connectivity features. In a standard multisector setup, I use this model to provide analytical expressions linking aggregate volatility to the network structure of input trade. I show that the presence of sectoral hubs - by coupling production decisions across sectors - leads to fluctuations in aggregates.Aggregation; Business Cycles; Comovement; Input-Output; Multisector Growth Models; Networks; Technological Diversification.

The network origins of aggregate fluctuations

This paper argues that in the presence of intersectoral input-output linkages, microeconomic idiosyncratic shocks may lead to aggregate fluctuations. In particular, it shows that, as the economy becomes more disaggregated, the rate at which aggregate volatility decays is determined by the structure of the network capturing such linkages. Our main results provide a characterization of this relationship in terms of the importance of different sectors as suppliers to their immediate customers as well as their role as indirect suppliers to chains of downstream sectors. Such higher-order interconnections capture the possibility of "cascade effects" whereby productivity shocks to a sector propagate not only to its immediate downstream customers, but also indirectly to the rest of the economy. Our results highlight that sizable aggregate volatility is obtained from sectoral idiosyncratic shocks only if there exists significant asymmetry in the roles that sectors play as suppliers to others, and that the "sparseness" of the input-output matrix is unrelated to the nature of aggregate fluctuations.Business cycle, aggregate volatility, diversification, input-output linkages, intersectoral network, cascades

Mucosal and physiological responses of Atlantic salmon (Salmo salar) in brackish water RAS following peracetic acid-based disinfection

Dissertação de Mestrado Integrado em Medicina VeterináriaPeracetic acid (PAA), a strong oxidative disinfectant, is effective against several microorganisms at low concentrations, requires short contact time and degrades rapidly into innocuous residues, thus considered a promising option for routine disinfection in aquaculture production. However, comprehensive knowledge of the impacts of the oxidant PAA on fish health is required for its safe application. This study documented the physiological impacts of periodic PAA exposure in Atlantic salmon (Salmo salar) post-smolts reared in brackish water recirculating aquaculture system. Salmon were exposed to PAA at a concentration of 1 mg/L every 3 days over 6 weeks. Three extensive tissue samplings were conducted (before exposure, 22 and 45 days of periodic PAA exposure). In addition, a stress test was performed before exposure and 45 days post-exposure to assess the effects of periodic exposure during a secondary stress encounter. There was no clear pattern on the changes in plasma stress parameters throughout the exposure trial, except with the glucose level, which significantly decreased over time. Oxidative stress was likely triggered by periodic oxidant exposure, as indicated by the documented significant increase in plasma antioxidants. PAA-induced expression of genes encoding for antioxidants, cytokines, heat shock proteins and mucins demonstrated a tissue-specific pattern: downregulation was observed in the gills and olfactory rosette, upregulation occurred in the skin, and no changes in the liver. Periodic oxidant exposure resulted in histological changes in key mucosal organs (olfactory rosette, skin and gills); pathological alterations were predominant in the gills where cases of epithelial lifting, hypertrophy, hyperplasia and lamellar clubbing were the most commonly identified. Lastly, periodic oxidant exposure did not alter the ability of salmon to mount robust physiological stress responses to a secondary stressor. Collectively, the present study demonstrated that periodic PAA exposure constituted an environmental stressor for which salmon were capable of mounting adaptive responses, both at the systemic and mucosal levels. In addition, periodic PAA exposure promoted the maintenance of stable microbiological water quality and did not affect the biofilter performance. The consequences of this disinfection protocol underscored the potential of PAA as a routine oxidant-based disinfection in salmon RAS production.RESUMO - O ácido paracético (PAA), um desinfetante com fortes propriedades oxidantes, é eficaz contra diversos microrganismos a baixas concentrações, requer um curto tempo de contacto e degrada-se rapidamente em resíduos inócuos, sendo, portanto, considerado uma alternativa promissora para a desinfeção de rotina em aquacultura. No entanto, é necessário um extenso conhecimento relativo aos impactos do PAA na saúde dos peixes para garantir a sua utilização segura. Este estudo documentou as consequências fisiológicas da exposição periódica ao PAA em Salmão do Atlântico (Salmo salar) na fase “post-smolt”, produzido num sistema de recirculação em aquacultura (RAS) de água salobra. Os peixes foram expostos ao PAA a uma concentração de 1 mg/L a cada 3 dias durante 6 semanas. Foram realizadas três recolhas extensivas de tecidos (antes da exposição, e aos dias 22 e 45 de exposição periódica). Além disso, foi realizado um desafio de stress antes do início de exposição e no dia 45 de exposição para avaliar os efeitos da exposição periódica na resposta a um estímulo secundário de stress. Durante o estudo não foi observado nenhum padrão óbvio na evolução dos parâmetros plasmáticos de stress, excetuando os níveis de glucose, que desceram significativamente ao longo do tempo. O stress oxidativo foi induzido provavelmente pela exposição periódica ao oxidante, tal como indicado pelo aumento nos níveis de antioxidantes plasmáticos. A expressão dos genes que codificam antioxidantes, citoquinas, proteínas de choque térmico e mucinas revelou que existe um padrão tecidular específico em resposta ao PAA: foi registado um padrão de inibição nas brânquias e na roseta olfatória, um padrão de indução na pele, enquanto no fígado não foram registadas alterações. A exposição ao PAA provocou alterações histológicas nas brânquias, pele e roseta olfatória, sendo as alterações predominantemente observadas nas brânquias, onde as alterações mais comuns foram casos de edema epitelial, hipertrofia, hiperplasia e “lamelar clubbing”. A exposição periódica ao PAA não afetou a capacidade do salmão para estabelecer uma resposta fisiológica eficiente na presença de um estímulo indutor de stress. De forma geral, este estudo demonstrou que a exposição periódica ao PAA constituiu um estímulo stressante para o qual os peixes foram capazes de apresentar respostas adaptativas, tanto a nível sistémico como nas mucosas. Além disso, a exposição ao PAA promoveu a manutenção da qualidade microbiológica da água e não afetou a performance do biofiltro. As respostas observadas neste protocolo de desinfeção destacam o potencial do PAA como um desinfetante de rotina na produção de salmão em RAS.N/

Essays on New Economic Geography

EconomiaDoctoral Programme in Economic

Distributed admission control for QoS and SLS management

This article proposes a distributed admission control (AC) model based on on-line monitoring to manage the quality of Internet services and Service Level Specifications (SLSs) in class-based networks. The AC strategy covers intra- and interdomain operation, without adding significant complexity to the network control plane and involving only edge nodes. While ingress nodes perform implicit or explicit AC resorting to service-oriented rules for SLS and QoS parameters control, egress nodes collect service metrics providing them as inputs for AC. The end-to-end operation is viewed as a cumulative and repetitive process of AC and available service computation.We discuss crucial key points of the model implementation and evaluate its two main components: themonitoring process and the AC criteria. The results show that, using proper AC rules and safety margins, service commitments can be efficiently satisfied, and the simplicity and flexibility of the model can be explored to manage successfully QoS requirements of multiple Internet services.(undefined

Admission control in multiservice IP networks : architectural issues and trends

The trend toward the integration of current and emerging applications and services in the Internet has launched new challenges regarding service deployment and management. Within service management, admission control (AC) has been recognized as a convenient mechanism to keep services under controlled load and assure the required QoS levels, bringing consistency to the services offered. In this context, this article discusses the role of AC in multiservice IP networks and surveys current and representative AC approaches. We address and compare the architectural principles of these AC approaches and their main features, virtues and limitations that impact on the quality control of network services. We identify important design aspects that contribute to the successful deployment of flexible and scalable AC solutions in multiservice networks

Scheduling time-sensitive IP traffic

This article presents an hybrid priority queuing model based scheduler for real-time traffic differentiation. The proposed scheduler is designed as a mechanism to provide queuing delay differentiation among real-time traffic classes. The novel characteristic of the presented scheduler is the capability to simultaneously try to achieve an upper time limit for queuing delays and, under heavy load conditions, deny class starvation by providing an expectable differentiation schema for excess queuing delays. The attractiveness of the proposed scheduler is its hybrid differentiation capabilities based on a simple queue selection procedure. Additionally, the enhanced differentiation behavior of the scheduler is also highlighted as three distinct configuration modes are possible