The Effect of Foot and Mouth Disease on Trade and Prices in International Beef Markets

The paper develops and uses a two step quantitative model to analyze the effect of Foot and Mouth Disease (FMD) on international beef markets over time. Using monthly data from 1990-2002 for 7 major beef exporters and for 22 major beef importers, we use a probit equation to estimate the probability that country i exports to country j, taking account of foot and mouth status of exporter, sanitary policy of importer, beef quality, trade preferences, distance, and other factors affecting whether beef trade occurs. We then use OLS to estimate the export prices that are obtained for beef, taking account of beef quality, country per capita, trading preferences, region, per capita income, and a time trend, including terms to adjust for censorship in the first stage. Using the estimated equations, we compare the predicted change in trading partners and in the prices received by the two exporters in our sample that are not FMD free, Brazil and Uruguay, under the assumption that their status switches from having FMD to being FMD free. The model performs well. The results suggest that FMD continues to impede trade between many countries and does accordingly reduce the price received for beef from countries with FMD. Nonetheless, the "sanction" from FMD appears smaller than previously believed.International Relations/Trade,

Dynamics of three-body correlations in quenched unitary Bose gases

We investigate dynamical three-body correlations in the Bose gas during the earliest stages of evolution after a quench to the unitary regime. The development of few-body correlations is theoretically observed by determining the two- and three-body contacts. We find that the growth of three-body correlations is gradual compared to two-body correlations. The three-body contact oscillates coherently, and we identify this as a signature of Efimov trimers. We show that the growth of three-body correlations depends non-trivially on parameters derived from both the density and Efimov physics. These results demonstrate the violation of scaling invariance of unitary bosonic systems via the appearance of log-periodic modulation of three-body correlations

Band topology and quantum spin Hall effect in bilayer graphene

We consider bilayer graphene in the presence of spin orbit coupling, to assess its behavior as a topological insulator. The first Chern number $n$ for the energy bands of single and bilayer graphene is computed and compared. It is shown that for a given valley and spin, $n$ in a bilayer is doubled with respect to the monolayer. This implies that bilayer graphene will have twice as many edge states as single layer graphene, which we confirm with numerical calculations and analytically in the case of an armchair terminated surface. Bilayer graphene is a weak topological insulator, whose surface spectrum is susceptible to gap opening under spin-mixing perturbations. We also assess the stability of the associated topological bulk state of bilayer graphene under various perturbations. Finally, we consider an intermediate situation in which only one of the two layers has spin orbit coupling, and find that although individual valleys have non-trivial Chern numbers, the spectrum as a whole is not gapped, so that the system is not a topological insulator.Comment: 9 pages. 9 figures include

TURFs and ITQs: Collective vs. Individual Decision Making

While most of the attention in the scientific and policy literature on rights-based institutions has been devoted to Individual Transferable Quotas (ITQs), there are alternatives that involve different configurations of use rights. One such alternative is a space-based option commonly referred to as Territorial Use Rights Fisheries (TURFs). TURFs have been utilized in island fisheries off Southeast Asia for decades, and they have been well studied, particularly by anthropologists and sociologists. This paper discusses case studies of TURF organizations in Japan and Chile from an economics perspective. We discuss the historical origins of each system, outline the legal and institutional structures of the systems, and then discuss how each system manages nearshore coastal resources. We discuss similarities and differences across the many specific collective management structures adopted by Japanese and Chilean TURF organizations. We then discuss how outcomes differ from what might emerge under ITQs.Collective management, resource management, rights-based fishery management, TURFs, Environmental Economics and Policy, International Relations/Trade, Q22,

Non-hermitian topology as a unifying framework for the Andreev versus Majorana states controversy

Zero-energy Andreev levels in hybrid semiconductor-superconductor nanowires mimic all expected Majorana phenomenology, including 2 e2∕ h conductance quantisation, even where band topology predicts trivial phases. This surprising fact has been used to challenge the interpretation of various transport experiments in terms of Majorana zero modes. Here we show that the Andreev versus Majorana controversy is clarified when framed in the language of non-Hermitian topology, the natural description for quantum systems open to the environment. This change of paradigm allows one to understand topological transitions and the emergence of zero modes in more general systems than can be described by band topology. This is achieved by studying exceptional point bifurcations in the complex spectrum of the system’s non-Hermitian Hamiltonian. Within this broader topological classification, Majoranas from both conventional band topology and a large subset of Andreev levels at zero energy are in fact topologically equivalent, which explains why they cannot be distinguishedWe thank J. Cayao for useful discussions in the early stages of this work. Research supported by the Spanish Ministry of Science, Innovation and Universities through Grants PGC2018-097018-B-I00, FIS2015-65706-P, FIS2015-64654-P, FIS2016-80434-P (AEI/FEDER, EU), the FPI programme BES-2016-078122, the Ramón y Cajal programme Grants RYC-2011-09345, RYC-2013-14645, the María de Maeztu Programme for Units of Excellence in R&D (MDM-2014-0377), and the European Union’s Horizon 2020 research and innovation programme under the FETOPEN Grant Agreement No. 828948. We also acknowledge support from CSIC Research Platform on Quantum Technologies PTI-00