The Duration of Trade Revisited: Continuous-Time vs. Discrete-Time Hazards

The recent literature on the duration of trade has predominantly analyzed the determinants of trade flow durations using Cox proportional hazards models. The purpose of this paper is to show why it is inappropriate to analyze the duration of trade with continuous-time models such as the Cox model, and to propose alternative discrete-time models which are more suitable for estimation. Briefly, the Cox model has three major drawbacks when applied to large trade data sets. First, it faces problems in the presence of many tied duration times, leading to biased coefficient estimates and standard errors. Second, it is difficult to properly control for unobserved heterogeneity, which can result in spurious duration dependence and parameter bias. Third, the Cox model imposes the restrictive and empirically questionable assumption of proportional hazards. By contrast, with discrete-time models there is no problem handling ties; unobserved heterogeneity can be controlled for without difficulty; and the restrictive proportional hazards assumption can easily be bypassed. By replicating an influential study by Besedeš and Prusa from 2006, but employing discrete-time models as well as the original Cox model, we find empirical support for each of these arguments against the Cox model. Moreover, when comparing estimation results obtained from a Cox model and our preferred discrete-time specification, we find significant differences in both the predicted hazard rates and the estimated effects of explanatory variables on the hazard. In other words, the choice between models affects the conclusions that can be drawn.Duration of Trade; Continuous-Time versus Discrete-Time Hazard Models; Proportional Hazards; Unobserved Heterogeneity

Exploring the Duration of EU Imports

The objective of this paper is twofold. First, against the background of an existing empirical literature on the duration of trade which has found that international trade is often of strikingly short duration, we aim to establish whether or not EU imports from the rest of the world also are short-lived. Second, since there is at this point no clear commonly accepted theoretical explanation for these short trade durations, we seek to provide a thorough empirical description and analysis of the phenomenon, with the intention of thereby facilitating theoretical developments on the subject. We employ a rich data set of detailed imports to the EU15 countries from 140 exporters, covering the time period 1962-2006. Using these data, we begin by conducting a thorough descriptive analysis of the duration of EU imports. Thereafter, we perform a regression analysis using discrete-time duration models with proper controls for unobserved heterogeneity. We draw the conclusion that EU imports are indeed very short-lived – in fact, possibly more so than, for example, US imports. The median duration of EU imports is for example merely one year, and almost 60 percent of all spells cease during the first year of service. Among our empirical findings are (i) that the duration of trade remains stable across the long time period that we study; (ii) that short trade durations are the result of at least two processes: countries shifting between different suppliers but continuing to import a given product, and countries ceasing to import the product altogether; and (iii) that countries with a diversified export structure also will tend to have more long-lived export flows. In our formal regression, we are also able to find a set of explanatory variables that have statistically significant effects on the probability that trade flows die.Duration of Trade; Survival; European Union; Discrete-Time Hazard Models

Exploring the Long-Term Evolution of Trade Survival

Aiming to explore how the survival of trade flows has evolved over time, we analyze a rich data set of detailed imports to individual EU15 countries from 140 non-EU exporters, covering the period 1962–2006. We find that short duration is a persistent characteristic of trade throughout the extended time period that we study: in general only 40 percent of trade flows survive the first year of service, and this share has not changed much since the 1960s. However, this observed constancy is the result of two underlying trends that work in opposite directions. On the one hand, positive trends in several of the observed explanatory variables – which in turn influence the hazard of trade flows dying in a negative direction – imply that the hazard tends to decrease over calendar time. On the other hand, there is also a positive trend in the hazard due to calendar year-specific unobserved factors. Holding all observed determinants constant, the probability of a trade flow dying in its first year increases from 34% at the beginning of the period to 90% at the end.Duration of Trade; Survival; Entry and Exit; European Union; Discrete-Time Hazard Models

A Flexible Link Function for Discrete-Time Duration Models

This paper proposes a discrete-time hazard regression approach based on the relation between hazard rate models and excess over threshold models, which are frequently encountered in extreme value modelling. The proposed duration model employs a flexible link function and incorporates the grouped-duration analogue of the well-known Cox proportional hazards model and the proportional odds model as special cases. The theoretical setup of the model is motivated, and simulation results are reported to suggest that it performs well. The simulation results and an empirical analysis of US import durations also show that the choice of link function in discrete hazard models has important implications for the estimation results, and that severe biases in the results can be avoided when using a flexible link function as proposed in this study

Comparative Genomics of the Baltic Sea Toxic Cyanobacteria Nodularia spumigena UHCC 0039 and Its Response to Varying Salinity

Salinity is an important abiotic factor controlling the distribution and abundance of Nodularia spumigena, the dominating diazotrophic and toxic phototroph, in the brackish water cyanobacterial blooms of the Baltic Sea. To expand the available genomic information for brackish water cyanobacteria, we sequenced the isolate Nodularia spurn/germ UHCC 0039 using an Illumina-SMRT hybrid sequencing approach, revealing a chromosome of 5,294,286 base pairs (bp) and a single plasmid of 92,326 bp. Comparative genomics in Nostocales showed pronounced genetic similarity among Nodularia spumigena strains evidencing their short evolutionary history. The studied Baltic Sea strains share similar sets of CRISPR-Cas cassettes and a higher number of insertion sequence (IS) elements compared to Nodularia spumigena CENA596 isolated from a shrimp production pond in Brazil. Nodularia spumigena UHCC 0039 proliferated similarly at three tested salinities, whereas the lack of salt inhibited its growth and triggered transcriptome remodeling, including the up-regulation of five sigma factors and the down-regulation of two other sigma factors, one of which is specific for strain UHCC 0039. Down-regulated genes additionally included a large genetic region for the synthesis of two yet unidentified natural products. Our results indicate a remarkable plasticity of the Nodularia salinity acclimation, and thus salinity strongly impacts the intensity and distribution of cyanobacterial blooms in the Baltic Sea.Peer reviewe

Prognostics and Health Management (PHM) for astronauts: a collaboration project on the International Space Station

Long-duration missions bring numerous risks that must be understood and mitigated in order to keep astronauts healthy, rather than treat a diagnosed health disorder. Having a limited medical support from mission control center on space exploration missions, crew members need a personal health-tracking tool to predict and assess his/her health risks if no preventive measures are taken. This paper refines a concept employing technologies from Prognostics and Health Management (PHM) for systems, namely real-time health monitoring and condition-based health maintenance with predictive diagnostics capabilities. Mapping particular PHM-based solutions to some Human Health and Performance (HH&P) technology candidates, namely by NASA designation, the Autonomous Medical Decision technology and the Integrated Biomedical Informatics technology, this conceptual paper emphasize key points that make the concept different from that of both current conventional medicine and telemedicine including space medicine. The primary benefit of the technologies development for the HH&P domain is the ability to successfully achieve affordable human space missions to Low Earth Orbit (LEO) and beyond. Space missions on the International Space Station (ISS) program directly contribute to the knowledge base and advancements in the HH&P domain, thanks to continued operations on the ISS, a unique human-tended test platform and the only test bed within the space environment. The concept is to be validated on the ISS, the only “test bed” on which to prepare for future manned exploration missions. The paper authors believe that early self-diagnostic coupled with autonomous identification of proper preventive responses on negative trends are critical in order to keep astronauts healthy

Evidence for the rapid expansion of microRNA-mediated regulation in early land plant evolution

BACKGROUND: MicroRNAs (miRNAs) are regulatory RNA molecules that are specified by their mode of action, the structure of primary transcripts, and their typical size of 20–24 nucleotides. Frequently, not only single miRNAs but whole families of closely related miRNAs have been found in animals and plants. Some families are widely conserved among different plant taxa. Hence, it is evident that these conserved miRNAs are of ancient origin and indicate essential functions that have been preserved over long evolutionary time scales. In contrast, other miRNAs seem to be species-specific and consequently must possess very distinct functions. Thus, the analysis of an early-branching species provides a window into the early evolution of fundamental regulatory processes in plants. RESULTS: Based on a combined experimental-computational approach, we report on the identification of 48 novel miRNAs and their putative targets in the moss Physcomitrella patens. From these, 18 miRNAs and two targets were verified in independent experiments. As a result of our study, the number of known miRNAs in Physcomitrella has been raised to 78. Functional assignments to mRNAs targeted by these miRNAs revealed a bias towards genes that are involved in regulation, cell wall biosynthesis and defense. Eight miRNAs were detected with different expression in protonema and gametophore tissue. The miRNAs 1–50 and 2–51 are located on a shared precursor that are separated by only one nucleotide and become processed in a tissue-specific way. CONCLUSION: Our data provide evidence for a surprisingly diverse and complex miRNA population in Physcomitrella. Thus, the number and function of miRNAs must have significantly expanded during the evolution of early land plants. As we have described here within, the coupled maturation of two miRNAs from a shared precursor has not been previously identified in plants

Auswirkungen von Arbeitslosigkeit auf die Familie

Der Beitrag referiert Anlage und wesentliche Befunde einer empirischen Erhebung vom Herbst 1988 bei arbeitslosen Vätern sowie deren Frauen und Kindern in zwei Arbeitsämtern Nordrhein-Westfalens. Insgesamt wurden in 206 Haushalten 410 Personen interviewt. "Im Zentrum der Analyse stehen die Formen der Betroffenheit und des Umgangs mit der verlorenen Arbeit bzw. der gewonnenen Freizeit. Durch eine Faktorenanalyse werden drei typische 'Verarbeitungsformen' identifiziert. Sie unterscheiden sich darin, daß auch positive Aspekte, soziale Isolierung oder gestörtes Selbstwertgefühl eine besondere Rolle spielen. Die einschneidenden Folgewirkungen von Arbeitslosigkeit auf die Männer und ihre Angehörigen erweisen sich für die drei Gruppen als durchaus verschiedenartig. Das betrifft - unabhängig von der Dauer der Arbeitslosigkeit - den Grad der Belastung durch das Mehr an freier Zeit und das veränderte Muster der Aktivitäten, aber auch die Partnerbeziehungen und das Verhältnis zu den Kindern. Die Untersuchung liefert Belege für die These, daß in vielen Fällen die Familie nicht zur Stabilisierung und Reintegration des Arbeitslosen beizutragen vermag, sondern durch das Zusammenwirken von materiellen und psychosozialen Belastungen eher überfordert wird." (IAB2)arbeitslose Männer, Arbeitslosigkeit - Auswirkungen, Familie, psychosoziale Faktoren, soziale Beziehungen, Freizeitverhalten, Nordrhein-Westfalen, Bundesrepublik Deutschland

Light-harvesting antenna function of phycoerythrin in Prochlorococcus marinus

AbstractProchlorococcus marinus strain CCMP 1375 is the sole prokaryote to possess phycoerythrin in addition to (divinyl-)chlorophyll a/b binding antenna complexes. Here we demonstrate, employing a spectrofluorimetric assay, that phycoerythrin serves a light-harvesting antenna function (transfers energy to chlorophylls)