Showing papers by "Hampshire College published in 1994"

Experimental realization of any discrete unitary operator.

Abstract: An algorithmic proof that any discrete finite-dimensional unitary operator can be constructed in the laboratory using optical devices is given. Our recursive algorithm factorizes any N\ifmmode\times\else\texttimes\fi{}N unitary matrix into a sequence of two-dimensional beam splitter transformations. The experiment is built from the corresponding devices. This also permits the measurement of the observable corresponding to any discrete Hermitian matrix. Thus optical experiments with any type of radiation (photons, atoms, etc.) exploring higher-dimensional discrete quantum systems become feasible.

Diel oxygen dynamics and anoxic events in an eutrophic estuary of Waquoit Bay, Massachusetts

Abstract: As a result of nutrient loading from septic systems, a thick canopy of macroalgae covers the bottom of Waquoit Bay, an embayment on Cape Cod, Massachusetts. Using automated conductivity-temperature-oxygen recorders and manual profiles, we measured diel water column O2 changes during summer in the Childs River, the estuary of the bay with the highest housing density. At dawn in midsummer, bottom waters in the Childs River are chronically hypoxic due to high rates of benthic respiration. On sunny days benthic photosynthesis drives bottom water O2 to 10–15 mg l−1 by afternoon. The extent of the daily O2 excursion is directly proportional to daily irradiance. Large diel O2 excursions in bottom water are due to limited mixing of surface and bottom water. Density stratification exceeded two sigma-t units 85% of the time during midsummer in the Childs River. Because of stratification, hypoxia and even anoxia occur in this estuary. The first of several anoxic events was observed in Waquoit Bay in 1988, and we have attempted to evaluate factors that trigger anoxia. High rates of benthic respiration result in anoxia when replenishment of O2 during the day is limited by insufficient light. Our analysis of meteorological records during two recent anoxic events shows that anoxia develops overnight in midsummer during periods of peak summertime temperatures after several days of cloudy, moderately calm weather. Similarly critical conditions existed most summers since 1975, yet anoxic events in the bay have not been reported historically. If climatic warming occurs, anoxic events in the bay may occur more frequently even if algal stocks remain unchanged. Eutrophication of Waquoit Bay is similar to many other embayments in populated coastal areas, and anoxic events may indicate a chronic growing problem in these important ecosystems. However, in shallow, stratified embayments, anoxia may be transient and easily missed without frequent monitoring.

Criticism, culture, and the automatic generation of artworks

Abstract: Researchers wishing to create computational systems that themselves generate artworks face two interacting challenges. The first is that the standards by which artistic output is judged are notoriously difficult to quantify. The larger AI community is currently involved in a rich internal dialogue on methodological issues, standards, and rigor, and hence murkiness with regard to the assessment of output must be faced squarely. The second challenge is that any artwork exists within an extraordinarily rich cultural and historical context, and it is rare that an artist who is ignorant of this context will produce acceptable works. In this paper we assert that these considerations argue for case-based AI/Art systems that take critical criteria as parameters. We describe an example system that produces new bebop jazz melodies from a case-base of melodies, using genetic programming techniques and a fitness function based on user-provided critical criteria. We discuss the role that such techniques may play in future work on AI and the arts.

Genetic programming and AI planning systems

Abstract: Genetic programming (GP) is an automatic programming technique that has recently been applied to a wide range of problems including blocks-world planning. This paper describes a series of illustrative experiments in which GP techniques are applied to traditional blocks-world planning problems. We discuss genetic planning in the context of traditional AI planning systems, and comment on the costs and benefits to be expected from further work.

The Terrorist Trap: America's Experience with Terrorism

Abstract: The World Trade Center bombing was only one more chapter in a long history of terrorist acts against the United States. The story told here, reaching back to the founding days of the Republic, is both instructive and alarming. Simon uncovers the dynamics of a deadly conflict that affects all of us. His in-depth interviews with terrorists and their victims, with reporters, government officials, and others bring to life a tale of presidents and terrorists, media and society, all entangled in the dramas of international violence. The Terrorist Trap traces the government response to terrorism from the days of Thomas Jefferson and the Barbary pirates to the confrontation of George Bush and Saddam Hussein. It explores the terrorist trap: the psychological, political, and social elements that make terrorism unlike any other conflict. With the end of the Cold War and the return of American hostages from Lebanon, many believed that terrorism was over. But Simon shows how terrorism grows out of political, economic, and social grievances that can never be fully resolved. Living with terrorism will be an inescapable part of life in the post-Cold War environment. Simon calls on officials to move away from the useless rhetoric of defeating terrorism and to focus instead on achievable goals in combatting this global problem.

Information Transfer with Two-state Two-particle Quantum Systems

Abstract: Any future quantum information machine will contain unitary operators and entangled particle states. The Hilbert space describing the action of the quantum information machine separates into a bosonic and a fermionic sector. Because the bosonic sector is of higher dimension, it is always possible to encode more information into a multiboson state than into a multifermion state, given the same complexity, that is unitary representation, of the quantum information machine. This is explicitly studied for the case of two particles defined in two modes. There the beam splitter is a generic representation of any U(2) matrix, and it has recently been shown that one can realize any N-dimensional unitary operator by successive application of such two-dimensional operators. The two-boson two-mode Hilbert space is of dimension three, and thus one can encode log23 = 1·57 bits of information into such an entangled state. Finally, some explicit schemes for creating and detecting the three possible, two-photon,...

Vapour-phase acid digestion of micro samples of biological material in a high-temperature, high-pressure asher for inductively coupled plasma atomic emission spectrometry

Abstract: This vapour-phase acid decomposition of small biological samples (50–165 mg) and concurrent purification of the reagent acid were achieved in a mini-quartz sample holder inserted in a commercial high-pressure digestion vessel. A 3.1 ml volume sample container was developed to hold the sample and to maximize the successful decomposition of a variety of biological samples. When biological standard reference materials were digested at 230 °C and 122 bar (1770 psi), the residual carbon content in the digested samples was less than 1.8 ± 0.1%. Inductively coupled plasma atomic emission spectrometric analysis of the digested materials for C, Ca, Cu, Cd, Fe, Mg, Mn and Zn provided good recoveries and low reagent blank values and demonstrated complete matrix decomposition.

The use of supervenience in dynamic-world planning

Abstract: This paper describes the use of supervenience in integrating planning and reaction in complex, dynamic environments. Supervenience is a form of abstraction with affinities both to abstraction in AI planning systems and to partitioning schemes in hierarchical control systems. The use of supervenience can be distilled to an easy-to-state constraint on the design of multilevel dynamic-world planning systems: world-knowledge up, goals down. We present the supervenience architecture which embodies this constraint, and contrast it to the subsumption architecture of Brooks. We describe the performance of an implementation of the supervenience architecture on a problem in the HomeBot domain, and we conclude with a discussion of the role that supervenience can play in future dynamic-world planning systems.

Ordering relations in human and machine planning

Abstract: Analytical results from AI planning research provide the motivation for this experimental study of ordering relationships in human planning. We examine timings of humans performing specific tasks from the AI planning literature and present evidence that normal human planners, like "state of the art" AI planning systems, use partial-order plan representations. We also describe ongoing experiments that are designed to shed light on the plan representations used by children and by adults with planning deficits due to brain damage. Several points of interest for collaboration between AI scientists and neuropsychologists are noted, as are impacts that we feel this research may have on future work in AI planning.

Evaluation of an elastomeric holographic index-matching medium.

Abstract: A transparent silicone elastomer is evaluated for suitability as an index-matching material for holography. Transparency, index of refraction, adhesion, dimensional stability, and optical activity are determined. Trials conducted in a student laboratory yield positive results.