The Macroeconomic Consequences of Disasters

The aim of this study is to describe the macroeconomic dynamics of natural disasters and their determinants in a large sample of disaster events, the first such attempt we are aware of. Our research shows that natural disasters have a statistically observable adverse impact on the macroeconomy in the short-run. Not surprisingly, costlier events cause more pronounced slowdowns in production. Yet, interestingly, developing countries, and smaller economies, face much larger output declines following a disaster of similar relative magnitude than do developed countries or bigger economies. A close study of the determinants of these adverse macroeconomic output costs reveals several interesting patterns. Countries with a higher literacy rate, better institutions, higher per capita income, higher degree of openness to trade, and higher levels of government spending are better able to withstand the initial disaster shock and prevent further spillovers into the macroeconomy. These all suggest an increased ability to mobilize resources for reconstruction. Financial conditions also seem to be of importance; countries with more foreign exchange reserves, and higher levels of domestic credit, but with less-open capital accounts appear more robust and better able to endure natural disasters, with less adverse spillover into domestic production.Natural disasters, growth

Length scale dependence of DNA mechanical properties

Although mechanical properties of DNA are well characterized at the kilo base-pair range, a number of recent experiments have suggested that DNA is more flexible at shorter length scales, which correspond to the regime that is crucial for cellular processes such as DNA packaging and gene regulation. Here, we perform a systematic study of the effective elastic properties of DNA at different length scales by probing the conformation and fluctuations of DNA from single base-pair level up to four helical turns, using trajectories from atomistic simulation. We find evidence that supports cooperative softening of the stretch modulus and identify the essential modes that give rise to this effect. The bend correlation exhibits modulations that reflect the helical periodicity, while it yields a reasonable value for the effective persistence length, and the twist modulus undergoes a smooth crossover---from a relatively smaller value at the single base-pair level to the bulk value---over half a DNA-turn.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Let

Random planar maps and graphs with minimum degree two and three

We find precise asymptotic estimates for the number of planar maps and graphs with a condition on the minimum degree, and properties of random graphs from these classes. In particular we show that the size of the largest tree attached to the core of a random planar graph is of order c log(n) for an explicit constant c. These results provide new information on the structure of random planar graphs.Comment: 32 page

Clusters, generating functions and asymptotics for consecutive patterns in permutations

We use the cluster method to enumerate permutations avoiding consecutive patterns. We reprove and generalize in a unified way several known results and obtain new ones, including some patterns of length 4 and 5, as well as some infinite families of patterns of a given shape. By enumerating linear extensions of certain posets, we find a differential equation satisfied by the inverse of the exponential generating function counting occurrences of the pattern. We prove that for a large class of patterns, this inverse is always an entire function. We also complete the classification of consecutive patterns of length up to 6 into equivalence classes, proving a conjecture of Nakamura. Finally, we show that the monotone pattern asymptotically dominates (in the sense that it is easiest to avoid) all non-overlapping patterns of the same length, thus proving a conjecture of Elizalde and Noy for a positive fraction of all patterns

The Brownian web is a two-dimensional black noise

The Brownian web is a random variable consisting of a Brownian motion starting from each space-time point on the plane. These are independent until they hit each other, at which point they coalesce. Tsirelson mentions this model in his paper "Scaling limit, Noise, Stability", along with planar percolation, in suggesting the existence of a two-dimensional black noise. A two-dimensional noise is, roughly speaking, a random object on the plane whose distribution is translation invariant and whose behavior on disjoint subsets is independent. Black means sensitive to the resampling of sets of arbitrarily small total area. Tsirelson implicitly asks: "Is the Brownian web a two-dimensional black noise?". We give a positive answer to this question, providing the second known example of such after the scaling limit of critical planar percolation.Comment: 16 Pages, 3 Figure

A solution to the tennis ball problem

We present a complete solution to the so-called tennis ball problem, which is equivalent to counting lattice paths in the plane that use North and East steps and lie between certain boundaries. The solution takes the form of explicit expressions for the corresponding generating functions. Our method is based on the properties of Tutte polynomials of matroids associated to lattice paths. We also show how the same method provides a solution to a wide generalization of the problem.Comment: 9 pages, Late

Prizes for Basic Research -- Human Capital, Economic Might and the Shadow of History

This paper studies the impact of global factors on patterns of basic research across countries and time. We rely on the records of major scientific awards, and on data dealing with global economic and historical trends. Specifically, we investigate the degree to which scale or threshold effects account for countries share of major prizes [Nobel, Fields, Kyoto and Wolf]. We construct a stylized model, predicting that lagged relative GDP of a country relative to the GDP of all countries engaging in basic research is an important explanatory variable of country's share of prizes. Scale effects imply that the association between the GDP share of a country and its prize share tends to be logistic -- above a threshold, there is a "take off" range, where the prize share increases at an accelerating rate with the relative GDP share of the country, until it reaches "maturity" stage. Our empirical analysis confirms the importance of lagged relative GDP in accounting for countries' prize shares, and the presence of "winner takes all" scale effect benefiting the leader. Using measures of casualties during the wars, we find that the only significant effect can be found for a lag of 3 decades – i.e., deaths in the war negatively impact the viability of basic research about 30 years after the fact. With more recent data, we document the growing importance of countries that used to be at the periphery of global research, possibly advancing towards the take off stage.Global economic trends, basic research, World War I and II, human capital, winner takes all