Set-Theoretic Types for Polymorphic Variants

Polymorphic variants are a useful feature of the OCaml language whose current definition and implementation rely on kinding constraints to simulate a subtyping relation via unification. This yields an awkward formalization and results in a type system whose behaviour is in some cases unintuitive and/or unduly restrictive. In this work, we present an alternative formalization of poly-morphic variants, based on set-theoretic types and subtyping, that yields a cleaner and more streamlined system. Our formalization is more expressive than the current one (it types more programs while preserving type safety), it can internalize some meta-theoretic properties, and it removes some pathological cases of the current implementation resulting in a more intuitive and, thus, predictable type system. More generally, this work shows how to add full-fledged union types to functional languages of the ML family that usually rely on the Hindley-Milner type system. As an aside, our system also improves the theory of semantic subtyping, notably by proving completeness for the type reconstruction algorithm.Comment: ACM SIGPLAN International Conference on Functional Programming, Sep 2016, Nara, Japan. ICFP 16, 21st ACM SIGPLAN International Conference on Functional Programming, 201

Some observations on arkshell clams, Noetia ponderosa and Anadara ovalis, and implications for fisheries management

Two species of arkshell or blood clams, Noetia ponderosa (ponderous ark) and Anadara ovalis (blood ark), have been harvested by watermen on the Eastern shore in Virginia since 1991. There is little information on the life history of these species in Virginia waters. The intensive harvesting of blood clams and paucity of data on important factors such as distribution, densities, growth rates, and size-age relationships present a problem for management of the fishery. The primary purpose of this study is to provide some basic information on blood clams for management of the fishery. We focused on age-size relationships and growth rates of clams. Some data were also collected on densities of blood clams and size-frequency distributions in fisheries and non-fisheries samples, as well as some morphometric data

A study of the arkshell clams, Noetia ponderosa (Say 1822) and Anadara ovalis (Bruguière 1789), in the oceanside lagoons and tidal creeks of Virginia

Two species of arkshell (\u27\u27blood\u27\u27) clams. Noelia ponderosa and Anadara ova/is. have recently been targeted by watermen on the eastern shore of Virginia for sale to both East and West Coast markets in the United States. Until 1991. fishermen caught both species in the harvest of oysters and hard clams, and discarded them as bycatch with little value. Very little is known about either species of blood clam. and preliminary data from a pilot study in 1993 indicated that they were being over-fished. We conducted a survey in September 1994 in the oceanside lagoon system along the eastern shore of Accomac and Nonhampton Counties, Virginia. and collected data on density. abundance. habitat preference. age-size and morphometric relationships. and mortality rates for both species of blood clams. as well as some ancillary data on the hard clam, Mercenaria mercenaria. The study provides baseline data for establishing management practices and regulations for the blood clam fishery. The total estimated abundance in the study area was about 16 million N. ponderosa and 6.4 mi llion A. ova/is. Of the clams taken in commercial catches on the oceanside of the eastern shore, M. mercenaria constitutes about 84%, N. ponderosa 15%, and A. ova/is I%. in our field survey, M. mercenaria was the most abundant species (72% of the total catch), followed by N. ponderosa ( 17%) and A. ova/is ( 11 %). Densities for blood clams averaged 0.35 clams m-2, or 3,500 clams per hectare. and were highest in shell and shell/mud substrate (I. I and 1.2 clams m- 2 • respectively). Growth studies and age-size data show that A. ova/is grows about twice as fast as N. ponderosa and that market-size N. ponderosa (about 56 mm in shell height) may be 8+ years old. We also present information on mortality rates and morphometric relationships for both species of blood clams, and recommendations for maintaining and enhancing the fishery

Search for Neutron Flux Generation in a Plasma Discharge Electrolytic Cell

Following some recent unexpected hints of neutron production in setups like high-voltage atmospheric discharges and plasma discharges in electrolytic cells, we present a measurement of the neutron flux in a configuration similar to the latter. We use two different types of neutron detectors, poly-allyl-diglicol-carbonate (PADC, aka CR-39) tracers and Indium disks. At 95% C.L. we provide an upper limit of 1.5 neutrons cm^-2 s^-1 for the thermal neutron flux at ~5 cm from the center of the cell. Allowing for a higher energy neutron component the largest allowed flux is 64 neutrons cm^-2 s^-1. This upper limit is two orders of magnitude smaller than what previously claimed in an electrolytic cell plasma discharge experiment. Furthermore the behavior of the CR-39 is discussed to point our possible sources of spurious signals.Comment: 4 pages, 3 figure

Thermal tolerance in embryos and larvae of the bay scallop Argopecten irradians under simulated power plant entrainment conditions

Thermal tolerance was tested in cleavage stages, trochophores and straight hinge larvae of the bay scallop Argopecten irradians. Experiments were designed to simulate larval entrainment in power plant cooling systems. An 11 (temperature) x 8 (time) matrix was used with temperatures ranging from 20.6 to 43.0 oc and exposure times from 1 min to 6 h. Pooled mortality data from triplicate experiments for each larval stage were subjected to stepwise regression analysis (Yarcsine % mortality on temperature and time). Equations derived from these analyses, comprising first, second and third order terms for temperature and time, were used to generate response surfaces relating mortality to temperature and exposure time. In general. higher mortalities were associated with higher temperatures and with longer time exposure at any one temperature. However, there was some evidence of cold shock in trochophore and straight hinge larvae, with elevated mortalities occurring at temperatures lower than the spawning temperature. There was a trend towards increased thermal tolerance in older larvae, although in general A. irradians showed the greatest sensitivity to thermal shock of the estuarine bivalves so far tested in our laboratory