XP. A Common Lisp Pretty Printing System

XP provides efficient and flexible support for pretty printing in Common Lisp. Its single greatest advantage is that it allows the full benefits of pretty printing to be obtained when printing data structures, as well as when printing program code. XP is efficient, because it is based on a linear time algorithm that uses only a small fixed amount of storage. XP is flexible, because users can control the exact form of the output via a set of special format directives. XP can operate on arbitrary data structures, because facilities are provided for specifying pretty printing methods for any type of object. XP also modifies the way abbreviation based on length, nesting depth, and circularity is supported so that they automatically apply to user-defined functions that perform output ??g., print functions for structures. In addition, a new abbreviation mechanism is introduced that can be used to limit the total numbers of lines printed

A Method, Based on Plans, for Understanding How a Loop Implements a Computation

This report describes research done at the Artificial Intelligence Laboratory of the Massachusetts Institute of Technology. Support for the laboratory's artificial intelligence research is provided in part by the Advanced Research Projects Agency of the Department of Defense under Office of Naval Research contract N00014-75-C-0643.The plan method analyzes the structure of a program. The plan which results from applying the method represents this structure by specifying how the parts of the program interact. This paper demonstrates the utility of the plan method by showing how a plan for a loop can be used to help prove the correctness of a loop. The plan does this by providing a convenient description of what the loop does. This paper also shows how a plan for a loop can be developed based on the code for the loop without the assistance of any commentary. This is possible primarily because most loops are built up in stereotyped ways according to a few fundamental plan types. An experiment is presented which supports the claim that a small number of plan types cover a large percentage of actual cases.MIT Artificial Intelligence Laboratory Department of Defense Advanced Research Projects Agenc

Cryptology and Data Communications

Research reported herein was conducted at the Artificial Intelligence Laboratory, a Massachusetts Institute of Technology research program supported in part by the Advanced Research Projects Agency of the Department of Defense and monitored by the office of Naval Research under contract N00014-75-C-0643.This paper is divided into two parts. The first part deals with cryptosystems and cryptanalysis. It surveys the basic information about cryptosystems and then addresses two specific questions. Are cryptosystems such as LUCIFER which are based on the ideas of Feistel and Shannon secure for all practical purposes? Is the proposed NBS standard cryptosystem secure for all practical purposes? This paper argues that the answer to the first question is "they might well be" and that the answer to the second is "no." The second part of this paper considers how a cryptosystem can be used to provide security of data transmission in a computer environment. It discusses the two basic aspects of security: secrecy and authentication. It then describes and discusses a specific proposal by Kent of a set of protocols designed to provide security through encryption. Finally, an alternate proposal is given in order to explore some of the other design choices which could have been made.MIT Artificial Intelligence Laboratory Department of Defense Advanced Research Projects Agenc

DETERMINING OPTIMAL REPLACEMENT AGE OF BEEF COWS IN THE PRESENCE OF STOCHASTIC ELEMENTS

Livestock Production/Industries,

Formalizing Reusable Software Components

This paper has been accepted by the ITT Workshop on Reusability in Programming, Newport RI, September 7-9, 1983.There has been a long-standing desire in computer science for a way of collecting and using libraries of standard software components. Unfortunately, there has been only limited success in actually doing this. We believe that the lack of success stems not from any resistance to the idea, nor from any lack of trying, but rather from the difficulty of choosing an appropriate formalism for representing components. In this paper we define five desiderata for a good formalization of reusable software components and discuss many of the formalisms which have been used for representing components in light of these desiderata. We then briefly describe a formalism we are developing — the Plan Calculus — which seeks to satisfy these desiderata by combining together the best features of prior formalisms.MIT Artificial Intelligence Laborator

Genes in the postgenomic era

We outline three very different concepts of the gene - 'instrumental', 'nominal', and 'postgenomic'. The instrumental gene has a critical role in the construction and interpretation of experiments in which the relationship between genotype and phenotype is explored via hybridization between organisms or directly between nucleic acid molecules. It also plays an important theoretical role in the foundations of disciplines such as quantitative genetics and population genetics. The nominal gene is a critical practical tool, allowing stable communication between bioscientists in a wide range of fields grounded in well-defined sequences of nucleotides, but this concept does not embody major theoretical insights into genome structure or function. The post-genomic gene embodies the continuing project of understanding how genome structure supports genome function, but with a deflationary picture of the gene as a structural unit. This final concept of the gene poses a significant challenge to conventional assumptions about the relationship between genome structure and function, and between genotype and phenotype

Diversity, Trends, Opportunities and Challenges in Australian Grasslands–Meeting the Sustainability and Productivity Imperatives of the Future?

Grassland production systems contribute 40% to Australia’s gross agricultural production value and utilise over 50% of its land area. Across this area a broad diversity of systems exist, but these can be broadly classified into four main production systems: 1. Pastoral grazing of mainly cattle at low intensity (i.e. \u3c 0.4 DSE/ha) on relatively unimproved native rangelands in the arid and semi-arid regions of northern and central Australia; 2. Crop-livestock systems in the semi-arid zone where livestock graze a mixture of pastures and crops which are often integrated; 3. High rainfall permanent pasture zone in the coastal hinterland and highlands and; 4. Dairy systems covering a broad range of environments and production intensities. A notable trend across these systems has been the replacement of wool sheep with beef cattle or meat sheep breeds, which has been driven by low wool prices. Although there is evidence that most of these systems have lifted production efficiencies over the past 30 years, total factor productivity growth has failed to match the decline in terms of trade. This has renewed attention on how research and development can help increase productivity. In addition, these industries are facing increasing scrutiny to improve their environmental performance and develop sustainable production practices. We propose several areas in which grasslands research and development might help provide gains in system productivity and sustainability. In particular, pasture productivity might be improved by filling gaps in the array of pastures available either through exploring new species or improving the adaptation and agronomic characteristics of species currently sown. Meanwhile there is a need to maintain efforts to overcome persistent and emerging constraints to pasture productivity. Improving livestock forage feed systems and more precise and lower cost management of grasslands would translate into improved utilisation and conversion of forage produced into livestock products. There is significant scope to capture value from the ecological services grasslands provide and mitigate greenhouse gas emissions from livestock production. Multi-purpose grasslands provide not only grazing for livestock but produce other food products such as grain which may also have potential to integrate livestock with cropping. However, reduced human research capacity in pasture science will challenge our ability to realise these potential opportunities unless efforts are made to attract and support a new generation of pasture scientists

Current Range in Lightning Return Strokes

In our investigation of breakdown waves, we use a one-dimensional, steady-state, constant velocity fluid model. This investigation involves breakdown waves for which the electric field force on electrons is in the opposite direction of wave propagation. The waves are considered to be shock fronted and the electron gas partial pressure is large enough to sustain the wave propagation. Our basic set of electron fluid-dynamical equations is composed of the equations for conservation of mass, momentum and energy, coupled with Poisson’s equation. This investigation involves breakdown waves for which a large current exists behind the shock front. The current behind the shock front alters the set of electron fluid-dynamical equations as well as the boundary conditions at the shock front. For the range of reported experimental current values (Wang et al. 1999), we have been able to solve the electron fluid dynamical equations within the dynamical transition region of the wave. Wave profile for electric field and electron velocity, number density and temperature within the dynamical transition region of the wave will be presente

The Disciplined Use of Simplifying Assumptions

Submitted to the ACM SIGSOFT Second Software Engineering Symposium: Workshop on Rapid Prototyping. Columbia, Maryland, April 19-21, 1982.Simplifying assumptions — everyone uses them but no one's programming tool explicitly supports them. In programming, as in other kinds of engineering design, simplifying assumptions are an important method for dealing with complexity. Given a complex programming problem, expert programmers typically choose simplifying assumptions which, though false, allow them to arrive rapidly at a program which addresses the important features of the problem without being distracted by all of its details. The simplifying assumptions are then incrementally retracted with corresponding modifications to the initial program. This methodology is particularly applicable to rapid prototyping because the main questions of interest can often be answered using only the initial program. Simplifying assumptions can easily be misused. In order to use them effectively two key issues must be addressed. First, simplifying assumptions should be chosen which simplify the design problems significantly without changing the essential character of the program which needs to be implemented. Second, the designer must keep track of all the assumptions he is making so that he can later retract them in an orderly manner. By explicitly dealing with these issues, a programming assistant system could directly support the use of simplifying assumptions as a disciplined part of the software development process.MIT Artificial Intelligence Laborator

Brown Dwarfs in Young Moving Groups from Pan-STARRS1. I. AB Doradus

Substellar members of young ($\lesssim$150 Myr) moving groups are valuable benchmarks to empirically define brown dwarf evolution with age and to study the low-mass end of the initial mass function. We have combined Pan-STARRS1 (PS1) proper motions with optical$-$IR photometry from PS1, 2MASS and $\textit{WISE}$ to search for substellar members of the AB Dor Moving Group within $\approx$50 pc and with spectral types of late-M to early-L, corresponding to masses down to $\approx$30 M$_{Jup}$ at the age of the group ($\approx$125 Myr). Including both photometry and proper motions allows us to better select candidates by excluding field dwarfs whose colors are similar to young AB~Dor Moving Group members. Our near-IR spectroscopy has identified six ultracool dwarfs (M6$-$L4; $\approx$30$-$100 M$_{Jup}$) with intermediate surface gravities (INT-G) as candidate members of the AB Dor Moving Group. We find another two candidate members with spectra showing hints of youth but consistent with field gravities. We also find four field brown dwarfs unassociated with the AB Dor Moving Group, three of which have INT-G gravity classification. While signatures of youth are present in the spectra of our $\approx$125 Myr objects, neither their $J-K$ nor $W1-W2$ colors are significantly redder than field dwarfs with the same spectral types, unlike younger ultracool dwarfs. We also determined PS1 parallaxes for eight of our candidates and one previously identified AB Dor Moving Group candidate. Although radial velocities (and parallaxes, for some) are still needed to fully assess membership, these new objects provide valuable insight into the spectral characteristics and evolution of young brown dwarfs.Comment: ApJ, accepte