The development and use of variables in mathematics and computer science

There are a wide variety of uses of variables in mathematics which we cope with in practice through conventions and tacit assumptions. Experience with computers has made us articulate, criticise and develop these assumptions much more carefully. Historically the term 'variable quantity' was introduced in the context of describing and calculating changing quantities which corresponded to phenomena in the observable world (e.g. the velocity of fluxion of a body moving under the inverse square law). The evolution of the concept has divorced it from these routes of reference and required us to establish the formal apparatus of interpretation and valuation. While the changes considered are highly structured this may be satisfactory, but computing power invites us to cope with change in vastly more complex, unstructured situations such as in simulation of 'real world' processes. We relate this challenge to the distinctive differences in the use of variables in mathematics and practical computing, and we develop a general framework in which all uses of variables can be described in a unified way

Experimenting with computing

AbstractWe distinguish two kinds of experimental activity: post-theory and exploratory. Post-theory experiment enjoys computer support that is well-aligned to the classical theory of computation. Exploratory experiment, in contrast, arguably demands a broader conception of computing. Empirical Modelling (EM) is proposed as a more appropriate conceptual framework in which to provide computational support for exploratory experiment. In the process, it promises to provide integrated computational support for both exploratory and post-theory experiment. We first sketch the motivation for EM and illustrate its potential for supporting experimentation, then briefly highlight the semantic challenge it poses and the philosophical implications

An experience-based approach to decision support systems

We identify and motivate a fundamental challenge for the effective use of decision support systems (DSS) in the future: how can we substantially improve the quality of interaction, and the degree of flexible engagement and integration, between humans and computers? We propose a new approach to using computers that is experience-based and human-centred, and that offers the potential to address this challenge through the construction of computer artefacts that are based upon the concepts of observables, dependency and agency

Worlds before and beyond words

The advent of computer-generated environments for simulating experience of the real world invites a reappraisal of the role of classical and neo-classical theories of computation (e.g. views of computation based on linguistic and logical frameworks.) To make more effective use of computers in connection with Virtual Reality requires a shift in emphasis towards computers as state representers rather than calculators, towards the construction and analysis of environments rather than documents and towards empirical rather than theoretical approaches to knowledge representation. This paper discusses the prospects for gaining new insights into empirical activity through the systematic construction of models (typically - but not necessarily - computer based) in which real world state, as perceived by a particular agent, is imitated directly through the use of suitable metaphors. Such activity is exemplified in the construction of engineering models and the development and calibration of scientific instruments. A characteristic ingredient of the modelling processes involved in these applications is correlation of the results of experiments and observations that are performed in parallel in a real world environment and in the associated physical (e.g. computer) model. Conventional computer programming paradigms are not well-suited for constructing models by empirical methods. Amongst widely used software tools, only spreadsheets are well adapted to imitating real world state as it is captured through observation and experiment. The philosophical ideas to be introduced in the paper have been developed in connection with practical case-studies and software tools that contribute to a long-term Empirical Modelling Project being pursued at the Computer Science Department at the University of Warwick. A key concept in this research programme is the development of agent-oriented models in which the dependencies between observables that are used for communication are specified using generalised spreadsheet principles

An All-Fiber, Modular, Compact Wind Lidar for Wind Sensing and Wake Vortex Applications

This paper discusses an innovative, compact and eyesafe coherent lidar system developed for wind and wake vortex sensing applications. With an innovative all-fiber and modular transceiver architecture, the wind lidar system has reduced size, weight and power requirements, and provides enhanced performance along with operational elegance. This all-fiber architecture is developed around fiber seed laser coupled to uniquely configured fiber amplifier modules. The innovative features of this lidar system, besides its all fiber architecture, include pulsewidth agility and user programmable 3D hemispherical scanner unit. Operating at a wavelength of 1.5457 microns and with a PRF of up to 20 KHz, the lidar transmitter system is designed as a Class 1 system with dimensions of 30"(W) x 46"(L) x 60"(H). With an operational range exceeding 10 km, the wind lidar is configured to measure wind velocities of greater than 120 m/s with an accuracy of +/- 0.2 m/s and allow range resolution of less than 15 m. The dynamical configuration capability of transmitted pulsewidths from 50 ns to 400 ns allows high resolution wake vortex measurements. The scanner uses innovative liquid metal slip ring and is built using 3D printer technology with light weight nylon. As such, it provides continuous 360 degree azimuth and 180 degree elevation scan angles with an incremental motion of 0.001 degree. The lidar system is air cooled and requires 110 V for its operation. This compact and modular lidar system is anticipated to provide mobility, reliability, and ease of field deployment for wind and wake vortex measurements. Currently, this wind lidar is undergoing validation tests under various atmospheric conditions. Preliminary results of these field measurements of wind characteristics that were recently carried out in Colorado are discussed

Rotation Grazing Demonstrations With Beef Cows on HEL - Adams County Conservation Reserve Program (CRP) Project

Two grazing systems were demonstrated on Conservation Reserve Program (CRP) land in southwestern Iowa near Corning in the summers of 1991, 1992, 1993, 1994, and 1995. This report summarizes the 1995 data and compares them to results from the four previous years. The systems, a 13-paddock intensive-rotational grazing system and a 4-paddock more traditional rotation, both established in 1991, are aimed at showing economically sustainable grass alternatives for steeply sloping (9-14% slope), highly erodible land (HEL) once the 10-year CRP ends. In a 147-day grazing season in 1995, nursing crossbred calves with no creep gained 2.36 pounds and 2.38 pounds per day on the 13- and 4-paddock systems, respectively. The rotations were stocked at 1.65 acres per cow-calf pair on the 13-paddock system and 1.72 acres per pair on the 4-paddock system. This produced 210.2 pounds of calf gain per acre on the 13-paddock system and 203.2 pounds of calf gain per acre on the 4- paddock system.. Similar calves gained 2.37 pounds and 2.50 pounds per day for 155 days, yielding a total gain per acre of 222.7 pounds on the 13-paddock system and 224.9 pounds on the 4-paddock system in 1994. Results for 1992 remain the highest from both systems in the five years of grazing, with calf gain per head per day at 2.45 for 155 days netting 241.9 pounds per acre on the 13- paddock system and calf gain per head per day at 2.38 for 154 days on the 4-paddock system yielding 263.6 pounds per acre. Cows maintained both their weight and condition scores in both systems again in 1995. A third system, the 18-paddock intensive-rotational grazing system, was stocked with stocker steers in 1995, and the results are reported in a second article in the 1996 ISU Beef Research Report entitled “Intensive- Rotational Grazing Steers on Highly Erodible Land at the Adams County CRP Project.” Concerning grazing management, paddocks were grazed four, five, or six times in the 13-paddock intensive- rotational grazing system during the 147-day grazing season of 1995. This number of times grazed per paddock was nearly equal to times grazed per paddock in 1994. However, several paddocks were subdivided temporarily to equalize paddock size and increase grazing uniformity. This increased the total number of cattle moves in the 13-paddock system from 78 in 1994 to 109 in 1995. The average length of stay on each paddock or subdivision of a paddock per grazing time was 1 to 2.2 days. This was less than in any of the other four grazing years in this project. The principle of not grazing more than half the standing forage during any one grazing period was closely followed in 1995. All paddocks in the 13-paddock system were also rested approximately the recommended 30 days between each grazing cycle in 1995

Supernova PTF12glz: a possible shock breakout driven through an aspherical wind

We present visible-light and ultraviolet (UV) observations of the supernova PTF12glz. The SN was discovered and monitored in near-UV and R bands as part of a joint GALEX and Palomar Transient Factory campaign. It is among the most energetic Type IIn supernovae observed to date (~10^51erg). If the radiated energy mainly came from the thermalization of the shock kinetic energy, we show that PTF12glz was surrounded by ~1 solar mass of circumstellar material (CSM) prior to its explosive death. PTF12glz shows a puzzling peculiarity: at early times, while the freely expanding ejecta are presumably masked by the optically thick CSM, the radius of the blackbody that best fits the observations grows at ~8000km/s. Such a velocity is characteristic of fast moving ejecta rather than optically thick CSM. This phase of radial expansion takes place before any spectroscopic signature of expanding ejecta appears in the spectrum and while both the spectroscopic data and the bolometric luminosity seem to indicate that the CSM is optically thick. We propose a geometrical solution to this puzzle, involving an aspherical structure of the CSM around PTF12glz. By modeling radiative diffusion through a slab of CSM, we show that an aspherical geometry of the CSM can result in a growing effective radius. This simple model also allows us to recover the decreasing blackbody temperature of PTF12glz. SLAB-Diffusion, the code we wrote to model the radiative diffusion of photons through a slab of CSM and evaluate the observed radius and temperature, is made available on-line.Comment: Sumbitted to ApJ. Comments are welcom

Processing Images from the Zwicky Transient Facility

The Zwicky Transient Facility is a new robotic-observing program, in which a newly engineered 600-MP digital camera with a pioneeringly large field of view, 47~square degrees, will be installed into the 48-inch Samuel Oschin Telescope at the Palomar Observatory. The camera will generate $\sim 1$~petabyte of raw image data over three years of operations. In parallel related work, new hardware and software systems are being developed to process these data in real time and build a long-term archive for the processed products. The first public release of archived products is planned for early 2019, which will include processed images and astronomical-source catalogs of the northern sky in the $g$ and $r$ bands. Source catalogs based on two different methods will be generated for the archive: aperture photometry and point-spread-function fitting.Comment: 6 pages, 4 figures, submitted to RTSRE Proceedings (www.rtsre.org

Ecology and management of the greater prairie-chicken

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