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Showing papers by "Massachusetts Institute of Technology published in 1987"


Journal ArticleDOI
TL;DR: This paper provides an introduction to the field of artificial neural nets by reviewing six important neural net models that can be used for pattern classification and exploring how some existing classification and clustering algorithms can be performed using simple neuron-like components.
Abstract: Artificial neural net models have been studied for many years in the hope of achieving human-like performance in the fields of speech and image recognition. These models are composed of many nonlinear computational elements operating in parallel and arranged in patterns reminiscent of biological neural nets. Computational elements or nodes are connected via weights that are typically adapted during use to improve performance. There has been a recent resurgence in the field of artificial neural nets caused by new net topologies and algorithms, analog VLSI implementation techniques, and the belief that massive parallelism is essential for high performance speech and image recognition. This paper provides an introduction to the field of artificial neural nets by reviewing six important neural net models that can be used for pattern classification. These nets are highly parallel building blocks that illustrate neural net components and design principles and can be used to construct more complex systems. In addition to describing these nets, a major emphasis is placed on exploring how some existing classification and clustering algorithms can be performed using simple neuron-like components. Single-layer nets can implement algorithms required by Gaussian maximum-likelihood classifiers and optimum minimum-error classifiers for binary patterns corrupted by noise. More generally, the decision regions required by any classification algorithm can be generated in a straightforward manner by three-layer feed-forward nets.

7,798 citations


Book
01 Jan 1987
TL;DR: Undergraduate and graduate classes in computer networks and wireless communications; undergraduate classes in discrete mathematics, data structures, operating systems and programming languages.
Abstract: Undergraduate and graduate classes in computer networks and wireless communications; undergraduate classes in discrete mathematics, data structures, operating systems and programming languages. Also give lectures to both undergraduate-and graduate-level network classes and mentor undergraduate and graduate students for class projects.

6,991 citations


Journal ArticleDOI
01 Oct 1987-Genomics
TL;DR: A computer package, called MAPMAKER, designed specifically for the construction of linkage maps in a number of organisms, including the human and several plants, and it is outlined the mapping strategies that have been used.

6,745 citations


Book
01 Jan 1987
TL;DR: The problems that face professionals (physicians, lawyers, architects) are often complex and lack "right answers." Skillful professional practice often depends less on factual knowledge than on the ability to reflect before taking action as discussed by the authors.
Abstract: My Personal Review: The problems that face professionals (physicians, lawyers, architects) are rarely straightforward and clear. They are complex and lack "right answers." Skillful professional practice often depends less on factual knowledge than on the ability to reflect before taking action. Yet most professional schools only teach theory and how to apply it to straightforward problems. Frankly, future professionals are being poorly equipped for the real world.

6,254 citations


Journal ArticleDOI
27 Feb 1987-Cell
TL;DR: This brief review of sequence data from embryogenesis, thrombosis, and lymphocyte help and killing is summarized and attempts to clarify the relationships among the members of this family of cell surface receptors.

4,229 citations


Proceedings ArticleDOI
01 Jan 1987
TL;DR: This work presents a polynomial-time algorithm that, given as a input the description of a game with incomplete information and any number of players, produces a protocol for playing the game that leaks no partial information, provided the majority of the players is honest.
Abstract: We present a polynomial-time algorithm that, given as a input the description of a game with incomplete information and any number of players, produces a protocol for playing the game that leaks no partial information, provided the majority of the players is honest. Our algorithm automatically solves all the multi-party protocol problems addressed in complexity-based cryptography during the last 10 years. It actually is a completeness theorem for the class of distributed protocols with honest majority. Such completeness theorem is optimal in the sense that, if the majority of the players is not honest, some protocol problems have no efficient solution [C].

3,579 citations


Journal ArticleDOI
TL;DR: By reducing the costs of coordination, information technology will lead to an overall shift toward proportionately more use of markets—rather than hierarchies—to coordinate economic activity.
Abstract: By reducing the costs of coordination, information technology will lead to an overall shift toward proportionately more use of markets—rather than hierarchies—to coordinate economic activity.

2,996 citations


Journal ArticleDOI
TL;DR: In this paper, a scaling analysis is performed to demonstrate that the effectiveness of actuators is independent of the size of the structure and evaluate various piezoelectric materials based on their effectiveness in transmitting strain to the substructure.
Abstract: This work presents the analytic and experimental development of piezoelectric actuators as elements of intelligent structures, i.e., structures with highly distributed actuators, sensors, and processing networks. Static and dynamic analytic models are derived for segmented piezoelectric actuators that are either bonded to an elastic substructure or embedded in a laminated composite. These models lead to the ability to predict, a priori, the response of the structural member to a command voltage applied to the piezoelectric and give guidance as to the optimal location for actuator placement. A scaling analysis is performed to demonstrate that the effectiveness of piezoelectric actuators is independent of the size of the structure and to evaluate various piezoelectric materials based on their effectiveness in transmitting strain to the substructure. Three test specimens of cantilevered beams were constructed: an aluminum beam with surface-bonded actuators, a glass/epoxy beam with embedded actuators, and a graphite/epoxy beam with embedded actuators. The actuators were used to excite steady-state resonant vibrations in the cantilevered beams. The response of the specimens compared well with those predicted by the analytic models. Static tensile tests performed on glass/epoxy laminates indicated that the embedded actuator reduced the ultimate strength of the laminate by 20%, while not significantly affecting the global elastic modulus of the specimen.

2,719 citations


Journal ArticleDOI
TL;DR: Techniques for simplifying decision trees while retaining their accuracy are discussed, described, illustrated, and compared on a test-bed of decision trees from a variety of domains.
Abstract: Many systems have been developed for constructing decision trees from collections of examples. Although the decision trees generated by these methods are accurate and efficient, they often suffer the disadvantage of excessive complexity and are therefore incomprehensible to experts. It is questionable whether opaque structures of this kind can be described as knowledge, no matter how well they function. This paper discusses techniques for simplifying decision trees while retaining their accuracy. Four methods are described, illustrated, and compared on a test-bed of decision trees from a variety of domains.

2,366 citations


Journal ArticleDOI
TL;DR: The diagnostic procedure presented in this paper is model-based, inferring the behavior of the composite device from knowledge of the structure and function of the individual components comprising the device.

2,199 citations


Journal ArticleDOI
TL;DR: In this paper, an adaptive robot control algorithm is derived, which consists of a PD feedback part and a full dynamics feed for the compensation part, with the unknown manipulator and payload parameters being estimated online.
Abstract: A new adaptive robot control algorithm is derived, which consists of a PD feedback part and a full dynamics feedfor ward compensation part, with the unknown manipulator and payload parameters being estimated online. The algorithm is computationally simple, because of an effective exploitation of the structure of manipulator dynamics. In particular, it requires neither feedback of joint accelerations nor inversion of the estimated inertia matrix. The algorithm can also be applied directly in Cartesian space.

Journal ArticleDOI
TL;DR: In this article, a deadlock-free routing algorithm for arbitrary interconnection networks using the concept of virtual channels is presented, where the necessary and sufficient condition for deadlock free routing is the absence of cycles in a channel dependency graph.
Abstract: A deadlock-free routing algorithm can be generated for arbitrary interconnection networks using the concept of virtual channels. A necessary and sufficient condition for deadlock-free routing is the absence of cycles in a channel dependency graph. Given an arbitrary network and a routing function, the cycles of the channel dependency graph can be removed by splitting physical channels into groups of virtual channels. This method is used to develop deadlock-free routing algorithms for k-ary n-cubes, for cube-connected cycles, and for shuffle-exchange networks.

Journal ArticleDOI
01 Apr 1987-Nature
TL;DR: Activation of T cells, which increases HIV expression up to 50-fold, correlated with induction of a DNA binding protein indistinguishable from a recognized transcription factor, called NF-κB, with binding sites in the viral enhancer.
Abstract: Human immunodeficiency virus (HIV) production from latently infected T lymphocytes can be induced with compounds that activate the cells to secrete lymphokines. The elements in the HIV genome which control activation are not known but expression might be regulated through a variety of DNA elements. The cis-acting control elements of the viral genome are enhancer and promoter regions. The virus also encodes trans-acting factors specified by the tat-III and art genes. We have examined whether products specific to activated T cells might stimulate viral transcription by binding to regions on viral DNA. Activation of T cells, which increases HIV expression up to 50-fold, correlated with induction of a DNA binding protein indistinguishable from a recognized transcription factor, called NF-kappa B, with binding sites in the viral enhancer. Mutation of these binding sites abolished inducibility. That NF-kappa B acts in synergy with the viral tat-III gene product to enhance HIV expression in T cells may have implications for the pathogenesis of AIDS (acquired immune deficiency syndrome).

Journal ArticleDOI
23 Jan 1987-Science
TL;DR: Test cases showed that the need for manual corrections during refinement of macromolecular crystal structures is reduced and the dynamics calculation moved residues that were misplaced by more than 3 angstroms into the correct positions without human intervention.
Abstract: Molecular dynamics was used to refine macromolecular structures by incorporating the difference between the observed crystallographic structure factor amplitude and that calculated from an assumed atomic model into the total energy of the system. The method has a radius of convergence that is larger than that of conventional restrained least-squares refinement. Test cases showed that the need for manual corrections during refinement of macromolecular crystal structures is reduced. In crambin, the dynamics calculation moved residues that were misplaced by more than 3 angstroms into the correct positions without human intervention.

Journal ArticleDOI
17 Jul 1987-Science
TL;DR: Together the hMR and hGR provide unexpected functional diversity in which hormone-binding properties, target gene interactions, and patterns of tissue-specific expression may be used in a combinatorial fashion to achieve complex physiologic control.
Abstract: Low-stringency hybridization with human glucocorticoid receptor (hGR) complementary DNA was used to isolate a new gene encoding a predicted 107-kilodalton polypeptide. Expression studies demonstrate its ability to bind aldosterone with high affinity and to activate gene transcription in response to aldosterone, thus establishing its identity as the human mineralocorticoid receptor (hMR). This molecule also shows high affinity for glucocorticoids and stimulates a glucocorticoid-responsive promoter. Together the hMR and hGR provide unexpected functional diversity in which hormone-binding properties, target gene interactions, and patterns of tissue-specific expression may be used in a combinatorial fashion to achieve complex physiologic control.

Book
22 Apr 1987
TL;DR: In this paper, the authors discuss related theories of recursively enumerable sets, degree of un-solvability and turing degrees in particular, and generalizations of recursion theory.
Abstract: Central concerns of the book are related theories of recursively enumerable sets, of degree of un-solvability and turing degrees in particular. A second group of topics has to do with generalizations of recursion theory. The third topics group mentioned is subrecursive computability and subrecursive hierarchies

Journal ArticleDOI
TL;DR: The use of 3A or 4A molecular sieves substantially increases the scope of the titanium(IV)-catalyzed asymmetric epoxidation of primary allylic alcohols as mentioned in this paper.
Abstract: The use of 3A or 4A molecular sieves (zeolites) substantially increases the scope of the titanium(IV)-catalyzed asymmetric epoxidation of primary allylic alcohols. Whereas without molecular sieves epoxidations employing only 5 to 10 mol % Ti(O-i-Pr)/sub 4/ generally lead to low conversion or low enantioselectivity, in the presence of molecular sieves such reactions generally lead to high conversion (>95%) and high enantioselectivity (90-95% ee). The epoxidations of 20 primary allylic alcohols are described. Especially noteworthy are the epoxidations of cinnamyl alcohol, 2-tetradecyl-2-propen-1-ol, allyl alcohol, and crotyl alcohol - compounds which heretofore had been considered difficult substrates for asymmetric epoxidation. In the case of allyl alcohol, the use of cumene hydroperoxide substantially increases both the reaction rate and the conversion, even in the absence of molecular sieves. In general, enantioselectivities are slightly depressed (by 1-5% ee) relative employing 50-100 mol % Ti(O-i-Pr)/sub 4/. The epoxidation of low molecular weight allylic alcohols is especially facilitated and, in conjunction with in situ derivatization, provides for the synthesis of many epoxy alcohol synthons which were previously difficult to obtain. The kinetic resolution of four secondary allylic alcohols with 10 mol % Ti(O-i-Pr)/sub 4/ is also described. The role of molecular sieves in the reaction andmore » the effects of variation in reaction stoichiometry, oxidant, and tartrate are discussed.« less

Book
25 Sep 1987
TL;DR: In this paper, the authors introduce a glossary of fast ions and fusion products, including fast ions, fast ion, and fast ion fusion products and their applications in the field of magnetic diagnostics.
Abstract: Preface to first edition Preface to second edition 1. Plasma diagnostics 2. Magnetic diagnostics 3. Plasma particle flux 4. Refractive-index measurements 5. Electromagnetic emission by free electrons 6. Electromagnetic radiation from bound electrons 7. Scattering of electromagnetic radiation 8. Neutral atom diagnostics 9. Fast ions and fusion products Appendices Glossary.

Journal ArticleDOI
TL;DR: In this paper, simple group-contribution methods are proposed to estimate eleven important physical properties of pure materials, and a common set of structural groups is employed to achieve high accuracy but not claimed to be as accurate as or more accurate than techniques in common use today.
Abstract: Simple group-contribution methods are proposed to estimate eleven important physical properties of pure materials. A common set of structural groups was employed. High accuracy is not claimed, but the proposed methods are often as accurate as or more accurate than techniques in common use today.

Journal ArticleDOI
TL;DR: All three variants of the classical problem of optimal policy computation in Markov decision processes, finite horizon, infinite horizon discounted, and infinite horizon average cost are shown to be complete for P, and therefore most likely cannot be solved by highly parallel algorithms.
Abstract: We investigate the complexity of the classical problem of optimal policy computation in Markov decision processes. All three variants of the problem finite horizon, infinite horizon discounted, and infinite horizon average cost were known to be solvable in polynomial time by dynamic programming finite horizon problems, linear programming, or successive approximation techniques infinite horizon. We show that they are complete for P, and therefore most likely cannot be solved by highly parallel algorithms. We also show that, in contrast, the deterministic cases of all three problems can be solved very fast in parallel. The version with partially observed states is shown to be PSPACE-complete, and thus even less likely to be solved in polynomial time than the NP-complete problems; in fact, we show that, most likely, it is not possible to have an efficient on-line implementation involving polynomial time on-line computations and memory of an optimal policy, even if an arbitrary amount of precomputation is allowed. Finally, the variant of the problem in which there are no observations is shown to be NP-complete.

Journal ArticleDOI
TL;DR: In this article, the potential contribution of the SST gradient-driven flow to the low-level (p not less than 700 mb) convergence over tropical oceans is determined using a simple one-layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically (consistent with the ECMWF analyzed data).
Abstract: The potential contribution of the SST gradient-driven flow to the low-level (p not less than 700 mb) convergence over tropical oceans is determined using a simple one-layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically (consistent with the ECMWF analyzed data). The influence of the layers above 700 mb is intentionally suppressed. The results of the study demonstrate the importance of taking account of the fact that cumulonimbus convection takes a small but finite time to adjust to low-level convergence. Failure to consider this effect leads to unreasonably large equatorial convergence.

Posted Content
TL;DR: The authors analyzes the statistical evidence bearing on whether transitory components account for a large fraction of the variance in common stock returns and concludes that explaining observed transitory component in stock prices on the basis of movements in required returns due to risk factors is likely to be difficult.
Abstract: This paper analyzes the statistical evidence bearing on whether transitory components account for a large fraction of the variance in common stock returns. The first part treats methodological issues involved in testing for transitory return components. It demonstrates that variance ratios are among the most powerful tests for detecting mean reversion in stock prices, but that they have little power against the principal interesting alternatives to the random walk hypothesis. The second part applies variance ratio tests to market returns for the United States over the 1871-1986 period and for seventeen other countries over the 1957-1985 period, as well as to returns on individual firms over the 1926- 1985 period. We find consistent evidence that stock returns are positively serially correlated over short horizons, and negatively autocorrelated over long horizons. The point estimates suggest that the transitory components in stock prices have a standard deviation of between 15 and 25 percent and account for more than half of the variance in monthly returns. The last part of the paper discusses two possible explanations for mean reversion: time varying required returns, and slowly-decaying "price fads" that cause stock prices to deviate from fundamental values for periods of several years. We conclude that explaining observed transitory components in stock prices on the basis of movements in required returns due to risk factors is likely to be difficult.

Journal ArticleDOI
TL;DR: In this article, the visual system decomposes shapes into parts, and uses a rule defining part boundaries rather than part shapes, exploiting a uniformity of nature, which allows an explanation of visual illusions.

Journal ArticleDOI
TL;DR: In this article, the authors present a model of trade in which comparative advantage, instead of being determined by underlying attributes of countries, evolves over time through learning-by-doing, where arbitrary patterns of specialization, once established, tend to become entrenched over time.

Journal ArticleDOI
TL;DR: Theorems that suggest that efficient general purpose planning with more expressive action representations is impossible are presented, and ways to avoid this problem are suggested.

Journal ArticleDOI
TL;DR: In this article, the authors present a review of the state-of-the-art work on hindered transport in liquid-filled pores of molecular dimensions, and the present status of this research is reviewed.
Abstract: Transport in liquid-filled pores of molecular dimensions plays an important role in membrane separations, in various forms of chromatography, and in catalysis, to name a few examples. A frequent observation is that if the pore dimensions are of the same order as those of a solute molecule, the apparent diffusion coefficient of that solute is much lower than in bulk solution. Likewise, rates of convective transport of such solutes are generally lower than the product of bulk concentration and volume flow rate. Thus, solute transport is typically “hindered” or restricted. A key objective of research on hindered transport is to be able to predict the applicable transport coefficients from such fundamental information as the size, shape, and electrical charge of the solutes and pores. The present status of this research is reviewed.

Book
01 Jan 1987
TL;DR: This book provides a laboratory in which the ideas presented in this book can be tested and applied to the synthesis of a great variety of systems, including practical applications involving parallel computation and image processing.
Abstract: Recently, cellular automata machines with the size, speed, and flexibility for general experimentation at a moderate cost have become available to the scientific community. These machines provide a laboratory in which the ideas presented in this book can be tested and applied to the synthesis of a great variety of systems. Computer scientists and researchers interested in modeling and simulation as well as other scientists who do mathematical modeling will find this introduction to cellular automata and cellular automata machines (CAM) both useful and timely.Cellular automata are the computer scientist's counterpart to the physicist's concept of 'field' They provide natural models for many investigations in physics, combinatorial mathematics, and computer science that deal with systems extended in space and evolving in time according to local laws. A cellular automata machine is a computer optimized for the simulation of cellular automata. Its dedicated architecture allows it to run thousands of times faster than a general-purpose computer of comparable cost programmed to do the same task. In practical terms this permits intensive interactive experimentation and opens up new fields of research in distributed dynamics, including practical applications involving parallel computation and image processing.Contents: Introduction. Cellular Automata. The CAM Environment. A Live Demo. The Rules of the Game. Our First rules. Second-order Dynamics. The Laboratory. Neighbors and Neighborhood. Running. Particle Motion. The Margolus Neighborhood. Noisy Neighbors. Display and Analysis. Physical Modeling. Reversibility. Computing Machinery. Hydrodynamics. Statistical Mechanics. Other Applications. Imaging Processing. Rotations. Pattern Recognition. Multiple CAMS. Perspectives and Conclusions.Tommaso Toffoli and Norman Margolus are researchers at the Laboratory for Computer Science at MIT. Cellular Automata Machines is included in the Scientific Computation Series, edited by Dennis Cannon.

Posted Content
TL;DR: In this article, the random walk model is strongly rejected for the entire sample period (1962-1985) and for all sub-periods for a variety of aggregate returns indexes and size-sorted portfolios.
Abstract: In this paper, we test the random walk hypothesis for weekly stock market returns by comparing variance estimators derived from data sampled at different frequencies. The random walk model is strongly rejected for the entire sample period (1962-1985) and for all sub-periods for a variety of aggregate returns indexes and size-sorted portfolios. Although the rejections are largely due to the behavior of small stocks, they cannot be ascribed to either the effects of infrequent trading or time-varying volatilities. Moreover, the rejection of the random walk cannot be interpreted as supporting a mean-reverting stationary model of asset prices, but is more consistent with a specific nonstationary alternative hypothesis.

Journal ArticleDOI
TL;DR: In this article, a method of accurately calculating transonic and low Reynolds number airfoil flows, implemented in the viscous-inviscid design/analysis code ISES, is presented.
Abstract: A method of accurately calculating transonic and low Reynolds number airfoil flows, implemented in the viscous-inviscid design/analysis code ISES, is presented. The Euler equations are discretized on a conservative streamline grid and are strongly coupled to a two-equation integral boundary-layer formulation, using the displacement thickness concept. A transition prediction formulation of the e type is derived and incorporated into the viscous formulation. The entire discrete equation set, including the viscous and transition formulations, is solved as a fully coupled nonlinear system by a global Newton method. This is a rapid and reliable method for dealing with strong viscous-inviscid interactions, which invariably occur in transonic and low Reynolds number airfoil flows. The results presented demonstrate the ability of the ISES code to predict transitioning separation bubbles and their associated losses. The rapid airfoil performance degradation with decreasing Reynolds number is thus accurately predicted. Also presented is a transonic airfoil calculation involving shock-induced separation, showing the robustness of the global Newton solution procedure. Good agreement with experiment is obtained, further demonstrating the performance of the present integral boundary-layer formulation.

Journal ArticleDOI
01 Jan 1987-Gene
TL;DR: A set of genomic plasmid banks was constructed using the centromere-containing yeast shuttle vector YCp50 to avoid the bias caused by differential sensitivity of sites to cleavage with Sau3A.