A theory of qualified types

AbstractThis paper describes a general theory of overloading based on a system of qualified types. The central idea is the use of predicates in the type of a term, restricting the scope of universal quantification. A corresponding semantic notion of evidence is introduced and provides a uniform framework for implementing applications of this system, including Haskell style type classes, extensible records and subtyping.Working with qualified types in a simple, implicitly typed, functional language, we extend the Damas-Milner approach to type inference. As a result, we show that the set of all possible typings for a given term can be characterized by a principal type scheme, calculated by a type inference algorithm

Topology of the Spin-polarized Charge Density in bcc and fcc Iron

We investigate the topology of the spin-polarized charge density in bcc and fcc iron. While the total spin-density is found to possess the topology of the non-magnetic prototypical structures, in some cases the spin-polarized densities are characterized by unique topologies; for example, the spin-polarized charge densities of bcc and high-spin fcc iron are atypical of any known for non-magnetic materials. In these cases, the two spin-densities are correlated: the spin-minority electrons have directional bond paths with deep minima in the minority density, while the spin-majority electrons fill these holes, reducing bond directionality. The presence of two distinct spin topologies suggests that a well-known magnetic phase transition in iron can be fruitfully reexamined in light of these topological changes. We show that the two phase changes seen in fcc iron (paramagnetic to low-spin and low-spin to high-spin) are different. The former follows the Landau symmetry-breaking paradigm and proceeds without a topological transformation, while the latter also involves a topological catastrophe.Comment: 5 pages, 3 figures. Phys. Rev. Lett. (in press

Archaeological Investigation at Slayton House, 18AP74, Annapolis, Maryland

Archaeological investigation at the Slayton House site in Annapolis revealed evidence of occupation of the lot since the early 18th century. The intact late 18th century ground surfaces on which John Ridout built the row houses, and subsequent changes in the landscape and use of the yard as work space in the 19th century were discovered. There was ample visible evidence of the early 20th century landscape and use of the yard as a pleasure garden when excavation was started. Deposits inside the house were quite disturbed, but there was evidence of the work done by the African Americans who lived there. A number of artifacts were found which may indicate the slaves and free African Americans were practicing African-related folk beliefs. No further investigations are recommended for the site. However, if severe or deep ground-disturbing activities were to take place on the property, they should be monitored by a qualified archaeologist

Competition, predation, and density-dependent mortality in demersal marine fishes

The relative roles of competition and predation in demographic density dependence are poorly known. A tractable experimental design to determine such effects and their interactions for demersal (seafloor oriented) fishes and similar sedentary species is cross-factoring multiple densities of new recruits with the presence and absence of predators. This design allows one to distinguish between density-dependent mortality due to competition alone, predation alone, or an interaction between the two, especially when supplemental field observations are available. To date, 14 species of marine fish have been examined with some variant of this design, and for 12 species predation was demonstrated to be the sole or major cause of density dependence. However, as competition may be slow acting relative to predation, the importance of competition can be underestimated in short-term experiments. On the Great Barrier Reef, we conducted a long-term field experiment in which multiple densities of new recruits of a planktivorous damselfish were cross-factored with the presence or absence of resident piscivorous fish on patch reefs. During the first 10 months, no density-dependent mortality was detected, regardless of whether resident predators were present or absent. By the end of the experiment at 17 months, per capita mortality was strongly density dependent and highly compensatory in both predator treatments; all reefs ultimately supported nearly the same adult density regardless of experimental treatment. Examination of treatment effect sizes suggested that competition was the main source of density-dependent mortality, with predation being merely a proximate agent of death. We hypothesize that predators were ineffective in this system compared with similar studies elsewhere because prey density was low relative to ample prey refuges provided by highly complex corals. Combined with previous studies, these findings indicate that density-dependent mortality in demersal marine fishes is often caused by interplay of predation and competition, whose roles may be altered by variation in habitat complexity and larval supply. These conclusions are relevant to marine fisheries models, which typically assume that density dependence is due solely to intraspecific competition

Archaeological Investigations Associated With The 1886 Hidalgo County Courthouse And Jail, Hidalgo County, Texas

EGV Architects Inc. (Client), on the behalf of the City of Hidalgo, contracted with Raba Kistner Environmental, Inc. (RKEI) to perform archaeological services in support of the on-going restoration to the Old Hidalgo County Courthouse and Jail located in Hidalgo, Hidalgo County, Texas. Services requested included the documentation of two historic cisterns present in the vicinity of the Courthouse and Old Jail Building and the mapping of foundations recently uncovered during the restoration of the Courthouse Building. The Courthouse and Jail were constructed simultaneously in 1886 by S.W. Brooks and were listed on the National Register of Historic Places (NRHP) in 1980 (THC 2016). The Courthouse originally served as the Hidalgo County Courthouse until the county seat was moved to Chapin (later Edinburg) in 1908. The original structure was two-stories, with a cupola. The roof, cupola, and entire second story were destroyed in a fire on Sunday January 18, 1920 (Le Meschacebe 1920). The building later served as an immigration and customs facility. Historic photographs and aerials depict a wall that surrounded the Jail and a probable guard house on the southeast corner within the wall. The tract of land the Courthouse and Jail currently stand contains at least two historic cisterns, one still extending above the existing ground surface (Cistern 1) and another that is currently buried below a functioning parking lot (Cistern 2). A third historic cistern, located at the northwestern corner of the courthouse, is also associated with the courthouse and jail, but is not located within the current project area. In addition to these cisterns, recent excavations for the installation of utilities also uncovered a series of shallowly-buried foundations. The network of these foundations was not been fully exposed. Their exact relationships to each other and to the standing structures on the Courthouse grounds are not well understood. The project had two principal goals. The first goal was to map the recently uncovered foundations that were discovered during the installation of utilities associated with the site. Secondly, RKEI was to collect cultural materials encountered if midden or trash deposits contemporaneous with the use of the Courthouse were revealed during the re-exposure of the foundations. A minimal number of cultural materials, consisting mostly of glass and ceramic, were observed during investigations. As a result of the project, RKEI archaeologists were able to uncover, map, photograph and profile several features within the project area. The edges of the known cistern just south of the jail (Cistern 1) ii were exposed to determine the cistern’s diameter. The buried cistern under the parking lot just east of the Jail (Cistern 2) was uncovered and profiled. The four corners of the original wall that surrounded the Jail were all exposed. The foundations of the guard house located at the southeast corner of the Jail wall were uncovered and documented. Finally, the original brick-lined storm water drains that led from both the Courthouse and Jail to the cistern extending above the existing ground surface just south of the Jail (Cistern 1) were exposed and documented. All exposed features were documented as archaeological site 41HG260. Since the project area is currently owned by a political subdivision of the state, the project fell under the Antiquities Code of Texas as administered by the Texas Historical Commission (THC). The proposed impacts to a property that is listed on the National Register had to conform to the requirements of Section 106 of the National Historic Preservation Act (NHPA) of 1966, as administered by the Texas Historical Commission. The monitoring was conducted under Texas Antiquities Permit No. 7808. Dr. Steve A. Tomka served as Principal Investigator, Mark P. Luzmoor served as Project Archaeologist, and Tomás Cruz served as field technician. Stephen Walker, Landscape Architect and volunteer on the project, aided with excavations and provided insight into the locations of features within the courthouse complex. All field records, photographs, and diagnostic cultural materials collected during investigations will be curated at the Center for Archaeological Research at the University of Texas at San Antonio

Electronic Selection Rules Controlling Dislocation Glide in bcc Metals

The validity of the structure-property relationships governing the deformation behavior of bcc metals was brought into question with recent {\it ab initio} density functional studies of isolated screw dislocations in Mo and Ta. These existing relationships were semiclassical in nature, having grown from atomistic investigations of the deformation properties of the groups V and VI transition metals. We find that the correct form for these structure-property relationships is fully quantum mechanical, involving the coupling of electronic states with the strain field at the core of long $a/2$ screw dislocations.Comment: 4 pages, 2 figure

Many-body Electronic Structure of Metallic alpha-Uranium

We present results for the electronic structure of alpha uranium using a recently developed quasiparticle self-consistent GW method (QSGW). This is the first time that the f-orbital electron-electron interactions in an actinide has been treated by a first-principles method beyond the level of the generalized gradient approximation (GGA) to the local density approximation (LDA). We show that the QSGW approximation predicts an f-level shift upwards of about 0.5 eV with respect to the other metallic s-d states and that there is a significant f-band narrowing when compared to LDA band-structure results. Nonetheless, because of the overall low f-electron occupation number in uranium, ground-state properties and the occupied band structure around the Fermi energy is not significantly affected. The correlations predominate in the unoccupied part of the f states. This provides the first formal justification for the success of LDA and GGA calculations in describing the ground-state properties of this material.Comment: 4 pages, 3 fihgure