Country Diversification, Product Ubiquity, and Economic Divergence

Countries differ markedly in the diversification of their exports. Products differ in the number of countries that export them, which we define as their ubiquity. We document a new stylized fact in the global pattern of exports: there is a systematic relationship between the diversification of a country’s exports and the ubiquity of its products. We argue that this fact is not implied by current theories of international trade and show that it is not a trivial consequence of the heterogeneity in the level of diversification of countries or of the heterogeneity in the ubiquity of products. We account for this stylized fact by constructing a simple model that assumes that each product requires a potentially large number of non-tradable inputs, which we call capabilities, and that a country can only make the products for which it has all the requisite capabilities. Products differ in the number and specific nature of the capabilities they require, as countries differ in the number/nature of capabilities they have. Products that require more capabilities will be accessible to fewer countries (i.e., will be less ubiquitous), while countries that have more capabilities will have what is required to make more products (i.e., will be more diversified). Our model implies that the return to the accumulation of new capabilities increases exponentially with the number of capabilities already available in a country. Moreover, we find that the convexity of the increase in diversification associated with the accumulation of a new capability increases when either the total number of capabilities that exist in the world increases or the average complexity of products, defined as the number of capabilities products require, increases. This convexity defines what we term as a quiescence trap, or a trap of economic stasis: countries with few capabilities will have negligible or no return to the accumulation of more capabilities, while at the same time countries with many capabilities will experience large returns - in terms of increased diversification - to the accumulation of additional capabilities. We calibrate the model to three different sets of empirical data and show that the derived functional forms reproduce the empirically observed distributions of product ubiquity, the relationship between the diversification of countries and the average ubiquity of the products they export, and the distribution of the probability that two products are co-exported. This calibration suggests that the global economy is composed of a relatively large number of capabilities – between 23 and 80, depending on the level of disaggregation of the data – and that products require on average a relatively large fraction of these capabilities in order to be produced. The conclusion of this calibration is that the world exists in a regime where the quiescence trap is strong

The Network Structure of Economic Output

Much of the analysis of economic growth has focused on the study of aggregate output. Here, we deviate from this tradition and look instead at the structure of output embodied in the network connecting countries to the products that they export. We characterize this network using four structural features: the negative relationship between the diversification of a country and the average ubiquity of its exports, and the non-normal distributions for product ubiquity, country diversification and product co-export. We model the structure of the network by assuming that products require a large number of non-tradable inputs, or capabilities, and that countries differ in the completeness of the set of capabilities they have. We solve the model assuming that the probability that a country has a capability and that a product requires a capability are constant and calibrate it to the data to find that it accounts well for all of the network features except for the heterogeneity in the distribution of country diversification. In the light of the model, this is evidence of a large heterogeneity in the distribution of capabilities across countries. Finally, we show that the model implies that the increase in diversification that is expected from the accumulation of a small number of capabilities is small for countries that have a few of them and large for those with many. This implies that the forces that help drive divergence in product diversity increase with the complexity of the global economy when capabilities travel poorly

Estimates of air–sea feedbacks on sea surface temperature anomalies in the southern ocean

Sea surface temperature (SST) air–sea feedback strengths and associated decay time scales in the Southern Ocean (SO) are estimated from observations and reanalysis datasets of SST, air–sea heat fluxes, and ocean mixed layer depths. The spatial, seasonal, and scale dependence of the air–sea heat flux feedbacks is mapped in circumpolar bands and implications for SST persistence times are explored. It is found that the damping effect of turbulent heat fluxes dominates over that due to radiative heat fluxes. The turbulent heat flux feedback acts to damp SSTs in all bands and spatial scales and in all seasons, at rates varying between 5 and 25 W m⁻² K⁻¹, while the radiative heat flux feedback has a more uniform spatial distribution with a magnitude rarely exceeding 5 W m⁻² K⁻¹. In particular, the implied net air–sea feedback (turbulent + radiative) on SST south of the polar front, and in the region of seasonal sea ice, is as weak as 5–10 W m⁻² K⁻¹ in the summertime on large spatial scales. Air–sea interaction alone thus allows SST signals induced around Antarctica in the summertime to persist for several seasons. The damping effect of mixed layer entrainment on SST anomalies averages to approximately 20 W m⁻² K⁻¹ across the ACC bands in the summer-to-winter entraining season and thereby reduces summertime SST persistence to less than half of that predicted by air–sea interaction alone (i.e., 3–6 months).National Science Foundation (U.S.). Frontiers in Earth System Dynamic

Pointing errors in solar absorption spectrometry - correction scheme and its validation

A method for quantification of sun-pointing inaccuracies in solar absorption spectrometry is presented along with a correction scheme for the resulting errors in trace gas vertical column or profile retrievals. A posteriori correction of pointing errors requires knowledge of both coordinates of the mispointing vector on the solar disk. In principle, quantitative information on the mispointing can be retrieved from Doppler shifts of solar lines derived from measured spectra. However, this yields only one component of the mispointing vector, namely the one which is perpendicular to the solar rotation axis. Missing information on the second vector component has hindered a posteriori correction of mispointing errors so far. Our idea to overcome this problem is to obtain estimates of both coordinates of the mispointing by combining subsequent measurements with differing orientations of the solar rotation axis relative to the zenith direction. An implementation of this original concept is demonstrated using measurements from the solar absorption Fourier transform infrared (FTIR) spectrometer at the Zugspitze (47.42° N, 10.98° E, 2964 m a.s.l.). Soundings in the September 2012 to September 2014 time interval were impacted by mispointing problems due to a non-optimum solar tracking optics configuration. They show a mean mispointing in zenith direction of -0.063°. This causes biases in vertical soundings of trace gases, e.g. -2.82 ppb in monthly means of dry-air column-averaged mole fractions of methane (XCH4). Measurements made with the more stable pre-September 2012 and post-September 2014 optics configurations show considerably smaller mispointing effects. Applying the mispointing correction, the April 2006-March 2014 XCH4 trend determined from Zugspitze measurements is reduced from 6.45 [5.84, 7.04] to 6.07 [5.55, 6.59] ppb yr-1. The correction thereby restores consistency with results from the nearby Garmisch FTIR site (47.48° N, 11.06° E, 743 m a.s.l.). The mispointing correction is applicable to solar absorption measurements in the mid infrared and near infrared. It will be of particular benefit for refining existing records of high-accuracy-and-precision greenhouse gas soundings for the purpose of improved trend analysis or source-sink inversions

Putting hydrodynamic interactions to work: tagged particle separation

Separation of magnetically tagged cells is performed by attaching markers to a subset of cells in suspension and applying fields to pull from them in a variety of ways. The magnetic force is proportional to the field gradient, and the hydrodynamic interactions play only a passive, adverse role. Here we propose using a homogeneous rotating magnetic field only to make tagged particles rotate, and then performing the actual separation by means of hydrodynamic interactions, which thus play an active role. The method, which we explore here theoretically and by means of numerical simulations, lends itself naturally to sorting on large scales.Comment: Version accepted for publication - Europhysics Letter

International Knowledge Diffusion and the Comparative Advantage of Nations

In this paper we document that the probability that a product is added to a country’s export basket is, on average, 65% larger if a neighboring country is a successful exporter of that same product. We interpret our result as evidence of international intra-industry knowledge diffusion. Our results are consistent with the overall consensus in the literature on technology spillovers: diffusion is stronger at shorter distances; is weaker for more knowledge-intensive products; and has become faster over time

Effect of Control Mode and Test Rate on the Measured Fracture Toughness of Advanced Ceramics

The effects of control mode and test rate on the measured fracture toughness of ceramics were evaluated by using chevron-notched flexure specimens in accordance with ASTM C1421. The use of stroke control gave consistent results with about 2% (statistically insignificant) variation in measured fracture toughness for a very wide range of rates (0.005 to 0.5 mm/min). Use of strain or crack mouth opening displacement (CMOD) control gave approx. 5% (statistically significant) variation over a very wide range of rates (1 to 80 m/m/s), with the measurements being a function of rate. However, the rate effect was eliminated by use of dry nitrogen, implying a stress corrosion effect rather than a stability effect. With the use of a nitrogen environment during strain controlled tests, fracture toughness values were within about 1% over a wide range of rates (1 to 80 micons/m/s). CMOD or strain control did allow stable crack extension well past maximum force, and thus is preferred for energy calculations. The effort is being used to confirm recommendations in ASTM Test Method C1421 on fracture toughness measurement