Quantifying the impact of weak, strong, and super ties in scientific careers

Scientists are frequently faced with the important decision to start or terminate a creative partnership. This process can be influenced by strategic motivations, as early career researchers are pursuers, whereas senior researchers are typically attractors, of new collaborative opportunities. Focusing on the longitudinal aspects of scientific collaboration, we analyzed 473 collaboration profiles using an ego-centric perspective which accounts for researcher-specific characteristics and provides insight into a range of topics, from career achievement and sustainability to team dynamics and efficiency. From more than 166,000 collaboration records, we quantify the frequency distributions of collaboration duration and tie-strength, showing that collaboration networks are dominated by weak ties characterized by high turnover rates. We use analytic extreme-value thresholds to identify a new class of indispensable `super ties', the strongest of which commonly exhibit >50% publication overlap with the central scientist. The prevalence of super ties suggests that they arise from career strategies based upon cost, risk, and reward sharing and complementary skill matching. We then use a combination of descriptive and panel regression methods to compare the subset of publications coauthored with a super tie to the subset without one, controlling for pertinent features such as career age, prestige, team size, and prior group experience. We find that super ties contribute to above-average productivity and a 17% citation increase per publication, thus identifying these partnerships - the analog of life partners - as a major factor in science career development.Comment: 13 pages, 5 figures, 1 Tabl

Easy and nearly simultaneous proofs of the Ergodic Theorem and Maximal Ergodic Theorem

We give a short proof of a strengthening of the Maximal Ergodic Theorem which also immediately yields the Pointwise Ergodic Theorem.Comment: Published at http://dx.doi.org/10.1214/074921706000000266 in the IMS Lecture Notes--Monograph Series (http://www.imstat.org/publications/lecnotes.htm) by the Institute of Mathematical Statistics (http://www.imstat.org

A step towards the Alekseevskii Conjecture

We provide a reduction in the classification problem for non-compact, homogeneous, Einstein manifolds. Using this work, we verify the (Generalized) Alekseevskii Conjecture for a large class of homogeneous spaces.Comment: 12 pages, proof of main result simplified, final version to appear in Math. Annale

Investment and Capital Constraints: Repatriations Under the American Jobs Creation Act

The American Jobs Creation Act (AJCA) significantly lowered US firms' tax cost when accessing their unrepatriated foreign earnings. Using this temporary shock to the cost of internal financing, we examine the role of capital constraints in firms' investment decisions. Controlling for the capacity to repatriate foreign earnings under the AJCA, we find that a majority of the funds repatriated by capital constrained firms were allocated to approved domestic investment. While unconstrained firms account for a majority of repatriated funds, no increase in investment resulted. Contrary to other examinations of the AJCA, we find little change in leverage and equity payouts.

Patterns of remnant discrete symmetries

We analyze patterns of remnant discrete symmetries that arise from U(1)^N theories by spontaneous breaking. We describe a simple, geometrical way to understand these patterns and provide methods for identifying the discrete symmetries and bringing them to the simplest possible form. Applications in GUT and string model building are briefly discussed.Comment: 14 pages, 2 figures, a related Mathematica package can be downloaded from http://einrichtungen.physik.tu-muenchen.de/T30e/codes/DiscreteBreaking

Isomorphism and embedding of Borel systems on full sets

A Borel system consists of a measurable automorphism of a standard Borel space. We consider Borel embeddings and isomorphisms between such systems modulo null sets, i.e. sets which have measure zero for every invariant probability measure. For every t>0 we show that in this category there exists a unique free Borel system (Y,S) which is strictly t-universal in the sense that all invariant measures on Y have entropy <t, and if (X,T) is another free system obeying the same entropy condition then X embeds into Y off a null set. One gets a strictly t-universal system from mixing shifts of finite type of entropy at least t by removing the periodic points and "restricting" to the part of the system of entropy <t. As a consequence, after removing their periodic points the systems in the following classes are completely classified by entropy up to Borel isomorphism off null sets: mixing shifts of finite type, mixing positive-recurrent countable state Markov chains, mixing sofic shifts, beta shifts, synchronized subshifts, and axiom-A diffeomorphisms. In particular any two equal-entropy systems from these classes are entropy conjugate in the sense of Buzzi, answering a question of Boyle, Buzzi and Gomez.Comment: 17 pages, v2: correction to bibliograph

Germany’s Current Account and Trade Surpluses A Technical Debate Enters the Geopolitical Limelight. Bertelsmann Stiftung GED Study April 2018

During the past decade, macroeconomic imbalances – typified by countries’ surplus or deficit of exports, currency, or capital – have moved to the fore of international economic policy debates. Global events and developments, such as China’s integration into the world economy, the 2008 financial crisis, and the Eurozone crisis, have created, and in some cases, compounded longstanding trade and investment asymmetries around the world. These imbalances have no single cause, but are fostered and magnified by the competitiveness of a country’s industries, domestic demand, corporate investment decisions, and tax and monetary policy, among other factors. In recent years, the widening gaps in countries’ trade relationships have become highly politicized, prompting policymakers to respond with measures ranging from formalized monitoring to punitive tariffs