Superfluid Fermi atomic gas as a quantum simulator for the study of neutron-star equation of state

We theoretically propose an idea to use an ultracold Fermi gas as a quantum simulator for the study of the neutron-star equation of state (EoS) in the low-density region. Our idea is different from the standard quantum simulator that heads for {\it perfect} replication of another system, such as a Hubbard model discussed in high-$T_{\rm c}$ cuprates. Instead, we use the {\it similarity} between two systems, and theoretically make up for the difference between them. That is, (1) we first show that the strong-coupling theory developed by Nozi\`eres-Schmitt Rink (NSR) can quantitatively explain the recent EoS experiment on a $^6$Li superfluid Fermi gas in the BCS (Bardeen-Cooper-Schrieffer)-unitary limit far below the superfluid phase transition temperature $T_{\rm c}$. This region is considered to be very similar to the low density region (crust regime) of a neutron star (where a nearly unitary $s$-wave neutron superfluid is expected). (2) We then theoretically compensate the difference that, while the effective range $r_{\rm eff}$ is negligibly small in a superfluid $^6$Li Fermi gas, it cannot be ignored ($r_{\rm eff}=2.7$ fm) in a neutron star, by extending the NSR theory to include effects of $r_{\rm eff}$. The calculated EoS when $r_{\rm eff}=2.7$ fm is shown to agree well with the previous neutron-star EoS in the low density region predicted in nuclear physics. Our idea indicates that an ultracold atomic gas may more flexibly be used as a quantum simulator for the study of other complicated quantum many-body systems, when we use, not only the experimental high tunability, but also the recent theoretical development in this field. Since it is difficult to directly observe a neutron-star interior, our idea would provide a useful approach to the exploration for this mysterious astronomical object.Comment: 29 pages, 7 figure

Taxonomic notes on Encephalartos ferox (Cycadales : Zamiaceae), with the description of a new subspecies from Mozambique

Continued work on the systematics of the genus Encephalartos has been conducted over a large area along the Mozambican coast to determine the infraspecific variation and taxonomic status of Encephalartos ferox populations. The northern extent of the species was also investigated based on anecdotal information that it might represent a new taxon. Several (45) vegetative and reproductive (ca. 40) characters were analysed and used to re-circumscribe E. ferox. Literature and iconographic citations are included, as is information on ecology, cytology and conservation as available. No specimens of E. ferox were located north of the Save River in the Sofala Province, Mozambique, and the northernmost population of the species was found to be anomalous. Accordingly a new subspecies, E. ferox subsp. emersus, is recognised based on its invariably emergent stems, shorter unarmed petiole length, shorter leaves, greater number and narrower leaflets (in seedlings as well) which are more closely spaced. Strobili and peduncles in subsp. emersus are shorter and narrower with strobili having a propensity towards yellow, while internally the megasporophylls are green, grading to white away from the outer surface. The IUCN Red List status is suggested as Critically Endangered A4d + B1a,b(v) + B2a,b(v), with the threat of illegal over-collection highlighted.Estudos contínuos sobre a sistemática do gênero Encephalartos já foram realizados sobre uma grande área ao longo da costa de Moçambique para determinar variações infra-específicas e estado taxonômico das populações de Encephalartos ferox. A extensão da espécie no norte também foi investigada, baseado em evidência anedótica que a espécie pode representar um novo grupo taxonômico. Vários (45) caracteres vegetativos e reprodutivos (ca. 40) foram analisados e usados para circunscrever Encephalartos ferox. Literatura e citações iconográficas estão incluídas, também informações sobre a ecologia, citologia e conservação como disponível. Espécimenes de Encephalartos ferox não foram encontrados norte do rio Save, na província da Sofala e as populações mais setentrionais foram consideradas anômalas. Consequentemente, uma nova subespécie, Encephalartos ferox subsp. emersus é reconhecida. Com caules invariavelmente emergentes; pecíolos mais curtos e desarmados; folhas mais curtas e quantidade maior de folíolos mais estreitos (em mudas também) e estreitamente espaçados. Estróbilos e pedúnculos de Encephalartos ferox subsp. emersus são mais curtos e estreitos, com estróbilos mais propensos para o amarelo, enquanto megasporophylls são verdes internamente, tornando brancos distante da superfície externa. O estado da espécie sobre a Lista Vermelha da IUCN é Perigo Crítico A4D + B1a,b(v) + B2a,b(v), onde a ameaça de coleção ilegal é destacada.University of Pretoria and the South African National Research Foundationhttp://www.mapress.com/phytotaxahb201