Definitional interpreters for higher-order programming languages

Abstract. Higher-order programming languages (i.e., languages in which procedures or labels can occur as values) are usually defined by interpreters that are themselves written in a programming language based on the lambda calculus (i.e., an applicative language such as pure LISP). Examples include McCarthy’s definition of LISP, Landin’s SECD machine, the Vienna definition of PL/I, Reynolds ’ definitions of GEDANKEN, and recent unpublished work by L. Morris and C. Wadsworth. Such definitions can be classified according to whether the interpreter contains higher-order functions, and whether the order of application (i.e., call by value versus call by name) in the defined language depends upon the order of application in the defining language. As an example, we consider the definition of a simple applicative programming language by means of an interpreter written in a similar language. Definitions in each of the above classifications are derived from one another by informal but constructive methods. The treatment of imperative features such as jumps and assignment is also discussed

The Meaning of Types From Intrinsic to Extrinsic Semantics

A definition of a typed language is said to be "intrinsic" if it assignsmeanings to typings rather than arbitrary phrases, so that ill-typedphrases are meaningless. In contrast, a definition is said to be "extrinsic"if all phrases have meanings that are independent of their typings,while typings represent properties of these meanings.For a simply typed lambda calculus, extended with recursion, subtypes,and named products, we give an intrinsic denotational semanticsand a denotational semantics of the underlying untyped language. Wethen establish a logical relations theorem between these two semantics,and show that the logical relations can be "bracketed" by retractionsbetween the domains of the two semantics. From these results, wederive an extrinsic semantics that uses partial equivalence relations

Energetic Impact of Jet Inflated Cocoons in Relaxed Galaxy Clusters

Jets from active galactic nuclei (AGN) in the cores of galaxy clusters have the potential to be a major contributor to the energy budget of the intracluster medium (ICM). To study the dependence of the interaction between the AGN jets and the ICM on the parameters of the jets themselves, we present a parameter survey of two-dimensional (axisymmetric) ideal hydrodynamic models of back-to-back jets injected into a cluster atmosphere (with varying Mach numbers and kinetic luminosities). We follow the passive evolution of the resulting structures for several times longer than the active lifetime of the jet. The simulations fall into roughly two classes, cocoon-bounded and non-cocoon bounded sources. We suggest a correspondence between these two classes and the Faranoff-Riley types. We find that the cocoon-bounded sources inject significantly more entropy into the core regions of the ICM atmosphere, even though the efficiency with which energy is thermalized is independent of the morphological class. In all cases, a large fraction (50--80%) of the energy injected by the jet ends up as gravitational potential energy due to the expansion of the atmosphere.Comment: 12 pages, Accepted for publication in Ap

50 Years with the Chicks, 1901-1950, 1951

A 34-page booklet tracing the history of the Memphis Chicks (originally Chickasaws) baseball team from 1901 to 1951.https://digitalcommons.memphis.edu/speccoll-pub-shelby/1034/thumbnail.jp

Time-Delayed Subsidies: Interspecies Population Effects in Salmon

Cross-boundary nutrient inputs can enhance and sustain populations of organisms in nutrient-poor recipient ecosystems. For example, Pacific salmon (Oncorhynchus spp.) can deliver large amounts of marine-derived nutrients to freshwater ecosystems through their eggs, excretion, or carcasses. This has led to the question of whether nutrients from one generation of salmon can benefit juvenile salmon from subsequent generations. In a study of 12 streams on the central coast of British Columbia, we found that the abundance of juvenile coho salmon was most closely correlated with the abundance of adult pink salmon from previous years. There was a secondary role for adult chum salmon and watershed size, followed by other physical characteristics of streams. Most of the coho sampled emerged in the spring, and had little to no direct contact with spawning salmon nutrients at the time of sampling in the summer and fall. A combination of techniques suggest that subsidies from spawning salmon can have a strong, positive, time-delayed influence on the productivity of salmon-bearing streams through indirect effects from previous spawning events. This is the first study on the impacts of nutrients from naturally-occurring spawning salmon on juvenile population abundance of other salmon species

Dynamic response of boundary‐layer turbulence to oscillatory shear

The temporal response of a well‐developed turbulent boundary layer to the superposition of oscillatory shear has been measured experimentally, over a wide range of frequencies. The response is primarily a periodic organization in magnitude of components of the turbulent velocity field at the forcing frequency. Oscillatory production of turbulence arises predominantly as a modulation of the mean production process in the parent boundary layer. Close to the wall, the relative phases of response of components of turbulent kinetic energy indicate that temporal redistribution of turbulent kinetic energy is driven by robust coherent motions of the underlying mean flow. The local directions of redistribution deduced from these measurements indicate a wall impingement (splatting) effect, consistent with characterizations from numerical simulation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70705/2/PFADEB-3-1-178-1.pd

Fully-Coupled Simulation of Cosmic Reionization. I: Numerical Methods and Tests

We describe an extension of the Enzo code to enable fully-coupled radiation hydrodynamical simulation of inhomogeneous reionization in large $\sim (100 Mpc)^3$ cosmological volumes with thousands to millions of point sources. We solve all dynamical, radiative transfer, thermal, and ionization processes self-consistently on the same mesh, as opposed to a postprocessing approach which coarse-grains the radiative transfer. We do, however, employ a simple subgrid model for star formation which we calibrate to observations. Radiation transport is done in the grey flux-limited diffusion (FLD) approximation, which is solved by implicit time integration split off from the gas energy and ionization equations, which are solved separately. This results in a faster and more robust scheme for cosmological applications compared to the earlier method. The FLD equation is solved using the hypre optimally scalable geometric multigrid solver from LLNL. By treating the ionizing radiation as a grid field as opposed to rays, our method is scalable with respect to the number of ionizing sources, limited only by the parallel scaling properties of the radiation solver. We test the speed and accuracy of our approach on a number of standard verification and validation tests. We show by direct comparison with Enzo's adaptive ray tracing method Moray that the well-known inability of FLD to cast a shadow behind opaque clouds has a minor effect on the evolution of ionized volume and mass fractions in a reionization simulation validation test. We illustrate an application of our method to the problem of inhomogeneous reionization in a 80 Mpc comoving box resolved with $3200^3$ Eulerian grid cells and dark matter particles.Comment: 32 pages, 23 figures. ApJ Supp accepted. New title and substantial revisions re. v

X-ray Line Diagnostics of Hot Accretion Flows around Black Holes

We compute X-ray emission lines from thermal plasma in hot accretion flows. We show that line profiles are strong probes of the gas dynamics, and we present line-ratio diagnostics which are sensitive to the distribution of mass with temperature in the flow. We show how these can be used to constrain the run of density with radius, and the size of the hot region. We also present diagnostics which are primarily sensitive to the importance of recombination versus collisional ionization, and which could help discriminate ADAFs from photoionization-dominated accretion disk coronae. We apply our results to the Galactic center source Sagittarius A* and to the nucleus of M87. We find that the brightest predicted lines are within the detection capability of current $X$-ray instruments.Comment: 16 pages, 1 table, 9 figures, accepted to Ap