Productivity and the decision to import and export: Theory and evidence

This paper develops an open economy model with heterogeneous final goods producers who simultaneously choose whether to export their output and whether to use imported intermediates. Using the theoretical model, we develop and estimate a structural empirical model that incorporates heterogeneity in productivity, transport costs, and other costs using Chilean plant-level data for a set of manufacturing industries. The estimated model is consistent with many key features of the data regarding productivity, exporting, and importing. We perform a variety of counterfactual experiments to assess quantitatively the positive and normative effects of barriers to trade in import and export markets. These experiments suggest that there are substantial gains in aggregate productivity and welfare due to trade. Furthermore, because of import and export complementarities, policies which inhibit the importation of foreign intermediates can have a large adverse effect on the exportation of final goods.[1]


The Import and Export of Cognitive Science

From its inception, a large part of the motivation for Cognitive Science has been the need for an interdisciplinary journal for the study of minds and intelligent systems. One threat to the interdisciplinarity of Cognitive Science, both the field and journal, is that it may become, or already be, too dominated by psychologists. In 2005, psychology was a keyword for 51% of submissions, followed distantly by linguistics (17%), artificial intelligence (13%), neuroscience (10%), computer science (9%), and philosophy (8%). The Institute for Scientific Information (ISI) gathers data not only on how individual articles cite one another, but also on macroscopic citation patterns among journals. Journals or sets of journals can be considered as proxies for fields. As fields become established, they often create journals. By studying the patterns of citations among journals that cite and are cited by Cognitive Science, we can better: 1) appreciate the scholarly ecology surrounding the journal and the journals role within this ecology, 2) establish competitor and alternate journals, and 3) determine the natural clustering of fields related to cognitive science.[2]


pH in the plant endomembrane system — an import and export business

pH homeostasis is an essential process in all plant cells and the maintenance of correct luminal pH in the compartments of the endomembrane system is important not only for secondary active transport but also for a variety of cellular functions including protein modification, sorting, and trafficking. Due to their electrogenicity primary H+-pumps cannot establish and control the often large proton-gradients single-handedly but require the co-action of other ion transporters that serve as either shunt conductances or proton-leaks. Here, I will thus focus on recent results that highlight the interplay of proton-pumps and proton-coupled transporters in controlling pH in the compartments of the plant endomembrane system.[3]

Nuclear import and export pathways

Macromolecules enter or leave the nucleus by using nuclear localization signals (NLS), or nuclear export signals (NES), respectively. Different types of NLS and NES are recognized directly or indirectly via adapters, by transport receptors. All transport receptors identified thus far are members of the same family and share an ability to shuttle between the nucleus and the cytoplasm, and to interact with the small GTPase Ran and with nucleoporins at the nuclear pore complex (NPC). The GTPase Ran regulates the interaction of transport receptors with either cargoes, or adapters, or nucleoporins and is crucial in providing directionality to nuclear import and export. Surprisingly, GTP hydrolysis by Ran is not required for translocation of some receptor/cargo complexes through the NPC.[4]


Nuclear Import and Export of Viruses and Virus Genomes

Many viruses replicate in the nucleus of their animal and plant host cells. Nuclear import, export, and nucleo-cytoplasmic shuttling play a central role in their replication cycle. Although the trafficking of individual virus proteins into and out of the nucleus has been well studied for some virus systems, the nuclear transport of larger entities such as viral genomes and capsids has only recently become a subject of molecular analysis. In this review, the general concepts emerging are discussed and a survey is provided of current information on both plant and animal viruses. Summarizing the main findings in this emerging field, it is evident that most viruses that enter or exit the nucleus take advantage of the cell’s nuclear import and export machinery. With a few exceptions, viruses seem to cross the nuclear envelope through the nuclear pore complexes, making use of cellular nuclear import and export signals, receptors, and transport factors. In many cases, they capitalize on subtle control systems such as phosphorylation that regulate traffic of cellular components into and out of the nucleus. The large size of viral capsids and their composition (they contain large RNA and DNA molecules for which there are few precedents in normal nuclear transport) make the processes unique and complicated. Prior capsid disassembly (or deformation) is required before entry of viral genomes and accessory proteins can occur through nuclear pores. Capsids of different virus families display diverse uncoating programs which culminate in genome transfer through the nuclear pores.[5]


Reference

[1] Kasahara, H. and Lapham, B., 2013. Productivity and the decision to import and export: Theory and evidence. Journal of international Economics, 89(2), pp.297-316.

[2] Goldstone, R. and Leydesdorff, L., 2009. The import and export of cognitive science. arXiv preprint arXiv:0911.3641.

[3] Schumacher, K., 2014. pH in the plant endomembrane system—an import and export business. Current Opinion in Plant Biology, 22, pp.71-76.

[4] Moroianu, J., 1999. Nuclear import and export pathways. Journal of cellular biochemistry, 75(S32), pp.76-83.

[5] Whittaker, G.R. and Helenius, A., 1998. Nuclear import and export of viruses and virus genomes. Virology, 246(1), pp.1-23.