Real classification of complex quadrics

AbstractCanonical forms are given for complex quadric surfaces (and conics) under real changes of variable. The basic idea is to use known results on pairs of real quadratic forms

The map behind a binomial coefficient matrix over ZpZ

AbstractThe pn×pn matrix over Z/pZ whose entries are i+jj for 0⩽i, j <pn expresses the operation f⊸f(1(1−x)) on functions Fpn→Fpn. This interpretation makes the behavior of the matrix transparent

Linear maps preserving reduced norms

AbstractIf a linear map between central simple algebras preserves reduced norms, it is an isomorphism or antiisomorphism followed by multiplication by an element of reduced norm 1

A review of water quality issues influencing the habitat quality in dugong protection areas

In August 1997, the Commonwealth and Queensland Governments established 16 coastal Dugong Protection Areas (DPAs) to reduce the threat of mesh nets to dugongs (Dugong dugon). The DPAs are situated in the Central and Mackay/Capricorn Sections of the Great Barrier Reef Marine Park (GBRMP) and the Hervey Bay–Great Sandy Strait region (Figure 1), and were enacted by Regulation No. 11 (1997) under the Queensland Fisheries Act 1994 and the Nature Conservation (Dugong) Conservation Plan 1999 under the Nature Conservation Act 1992. The establishment of DPAs was considered the key strategy to address the rapid decline of the Great Barrier Reef (GBR) dugong population south of Cooktown

Constraining the properties of neutron star crusts with the transient low-mass X-ray binary Aql X-1

Aql X-1 is a prolific transient neutron star low-mass X-ray binary that exhibits an accretion outburst approximately once every year. Whether the thermal X-rays detected in intervening quiescent episodes are the result of cooling of the neutron star or due to continued low-level accretion remains unclear. In this work we use Swift data obtained after the long and bright 2011 and 2013 outbursts, as well as the short and faint 2015 outburst, to investigate the hypothesis that cooling of the accretion-heated neutron star crust dominates the quiescent thermal emission in Aql X-1. We demonstrate that the X-ray light curves and measured neutron star surface temperatures are consistent with the expectations of the crust cooling paradigm. By using a thermal evolution code, we find that ~1.2-3.2 MeV/nucleon of shallow heat release describes the observational data well, depending on the assumed mass-accretion rate and temperature of the stellar core. We find no evidence for varying strengths of this shallow heating after different outbursts, but this could be due to limitations of the data. We argue that monitoring Aql X-1 for up to ~1 year after future outbursts can be a powerful tool to break model degeneracies and solve open questions about the magnitude, depth and origin of shallow heating in neutron star crusts.Comment: 14 pages, 5 figures, 3 tables, accepted to MNRA

The Distribution and Importance of Arthropods Associated with Agriculture and Forestry in Chile

Farm Management,

Recovery of critically endangered Nassau grouper (Epinephelus striatus) in the Cayman Islands following targeted conservation actions.

Many large-bodied marine fishes that form spawning aggregations, such as the Nassau grouper (Epinephelus striatus), have suffered regional overfishing due to exploitation during spawning. In response, marine resource managers in many locations have established marine protected areas or seasonal closures to recover these overfished stocks. The challenge in assessing management effectiveness lies largely in the development of accurate estimates to track stock size through time. For the past 15 y, the Cayman Islands government has taken a series of management actions aimed at recovering collapsed stocks of Nassau grouper. Importantly, the government also partnered with academic and nonprofit organizations to establish a research and monitoring program (Grouper Moon) aimed at documenting the impacts of conservation action. Here, we develop an integrated population model of 2 Cayman Nassau grouper stocks based on both diver-collected mark-resight observations and video censuses. Using both data types across multiple years, we fit parameters for a state-space model for population growth. We show that over the last 15 y the Nassau grouper population on Little Cayman has more than tripled in response to conservation efforts. Census data from Cayman Brac, while more sparse, show a similar pattern. These findings demonstrate that spatial and seasonal closures aimed at rebuilding aggregation-based fisheries can foster conservation success

Some genus 3 curves with many points

Using an explicit family of plane quartic curves, we prove the existence of a genus 3 curve over any finite field of characteristic 3 whose number of rational points stays within a fixed distance from the Hasse-Weil-Serre upper bound. We also provide an intrinsic characterization of so-called Legendre elliptic curves