Enhanced stability of the square lattice of a classical bilayer Wigner crystal

The stability and melting transition of a single layer and a bilayer crystal consisting of charged particles interacting through a Coulomb or a screened Coulomb potential is studied using the Monte-Carlo technique. A new melting criterion is formulated which we show to be universal for bilayer as well as for single layer crystals in the case of (screened) Coulomb, Lennard--Jones and 1/r^{12} repulsive inter-particle interactions. The melting temperature for the five different lattice structures of the bilayer Wigner crystal is obtained, and a phase diagram is constructed as a function of the interlayer distance. We found the surprising result that the square lattice has a substantial larger melting temperature as compared to the other lattice structures. This is a consequence of the specific topology of the defects which are created with increasing temperature and which have a larger energy as compared to the defects in e.g. a hexagonal lattice.Comment: Accepted for publication in Physical Review

First record of Rhabdoceras suessi (Ammonoidea, Late Triassic) from the Transylvanian Triassic Series of the Eastern Carpathians (Romania) and a review of its biochronology, paleobiogeography and paleoecology

Abstract The occurrence of the heteromorphic ammonoid Rhabdoceras suessi Hauer, 1860, is recorded for the first time in the Upper Triassic limestone of the Timon-Ciungi olistolith in the Rarău Syncline, Eastern Carpathians. A single specimen of Rhabdoceras suessi co-occurs with Monotis (Monotis) salinaria that constrains its occurrence here to the Upper Norian (Sevatian 1). It is the only known heteromorphic ammonoid in the Upper Triassic of the Romanian Carpathians. Rhabdoceras suessi is a cosmopolitan species widely recorded in low and mid-paleolatitude faunas. It ranges from the Late Norian to the Rhaetian and is suitable for high-resolution worldwide correlations only when it co-occurs with shorter-ranging choristoceratids, monotid bivalves, or the hydrozoan Heterastridium. Formerly considered as the index fossil for the Upper Norian (Sevatian) Suessi Zone, by the latest 1970s this species lost its key biochronologic status among Late Triassic ammonoids, and it generated a controversy in the 1980s concerning the status of the Rhaetian stage. New stratigraphic data from North America and Europe in the subsequent decades resulted in a revised ammonoid biostratigraphy for the uppermost Triassic, the Rhaetian being reinstalled as the topmost stage in the current standard timescale of the Triassic. The geographic distribution of Rhabdoceras is compiled from published worldwide records, and its paleobiogeography and paleoecology are discussed

Sistemas de equações de demanda por carnes no Brasil: especificação e estimação

Especificações alternativas do sistema de demanda quase ideal (AIDS) foram utilizadas para estimar as demandas agregadas das carnes bovina, suína e de frango e outros bens de consumo e as suas elasticidades no Brasil. Detectada a necessidade de se utilizar a variável tendência nas equações dos modelos, observou-se uma tendência de crescimento da demanda por carnes e de decrescimento da demanda por outros bens de consumo. A variável dummy para o Plano Real indicou que o mesmo não afetou as demandas. Com base nas elasticidades próprios-preços Marshallianas, as demandas por carnes são inelásticas e a demanda por outros bens de consumo é elástica. As elasticidades preços-cruzados Marshallianas e Hicksianas confirmaram que as carnes bovina, suína e de frango são bens substitutos. As elasticidades-gasto indicaram que todos os bens são normais, exceto a carne suína que é um bem inferior. Como é provável que o gasto com o consumo das famílias aumente ao longo do tempo, ceteris paribus, as elasticidades gasto indicam que a demanda por carnes perderá importância para os outros bens de consumo, que o consumo de carne bovina perderá importância para a carne de frango e que o consumo de carne de porco perderá importância para as outras carnes

The Effect of Government Advertising Policies on the Market Power of Cigarette Firms

We estimate market power among cigarette manufacturers over 1952–1984, a period of uniform pricing. We apply the Bresnahan approach; adjust it to the firm level; employ a dynamic model with habit persistence; and add an advertising equation, which helps identify the parameters, increase degrees of freedom, and constrain parameters so we can interpret our results at the firm level, despite the fact that the equations conform to what we might see in a market model. We consider effects of government interventions upon demand and market power and find, for instance, that the 1971 broadcast advertising ban decreased market power. Copyright Springer 2006Advertising policies, broadcast advertising ban, cigarettes, market power, JEL classification, L1, L51, L66, M37,