Últimos itens adicionados do Acervo: MIT - Massachusetts Institute of Technology

O Instituto de Tecnologia de Massachusetts (em inglês, Massachusetts Institute of Technology, MIT) é um centro universitário de educação e pesquisa privado localizado em Cambridge, Massachusetts, nos Estados Unidos. É considerado um dos melhores do mundo.

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Dense Depth Maps from Epipolar Images

Mellor, J.P.; Teller, Seth; Lozano-Perez, Tomas
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 13 p.; 9353299 bytes; 3015264 bytes; application/postscript; application/pdf
Português
Recovering three-dimensional information from two-dimensional images is the fundamental goal of stereo techniques. The problem of recovering depth (three-dimensional information) from a set of images is essentially the correspondence problem: Given a point in one image, find the corresponding point in each of the other images. Finding potential correspondences usually involves matching some image property. If the images are from nearby positions, they will vary only slightly, simplifying the matching process. Once a correspondence is known, solving for the depth is simply a matter of geometry. Real images are composed of noisy, discrete samples, therefore the calculated depth will contain error. This error is a function of the baseline or distance between the images. Longer baselines result in more precise depths. This leads to a conflict: short baselines simplify the matching process, but produce imprecise results; long baselines produce precise results, but complicate the matching process. In this paper, we present a method for generating dense depth maps from large sets (1000's) of images taken from arbitrary positions. Long baseline images improve the accuracy. Short baseline images and the large number of images greatly simplifies the correspondence problem...

Complex Feature Recognition: A Bayesian Approach for Learning to Recognize Objects

Viola, Paul
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 29 p.; 1626255 bytes; 694971 bytes; application/postscript; application/pdf
Português
We have developed a new Bayesian framework for visual object recognition which is based on the insight that images of objects can be modeled as a conjunction of local features. This framework can be used to both derive an object recognition algorithm and an algorithm for learning the features themselves. The overall approach, called complex feature recognition or CFR, is unique for several reasons: it is broadly applicable to a wide range of object types, it makes constructing object models easy, it is capable of identifying either the class or the identity of an object, and it is computationally efficient--requiring time proportional to the size of the image. Instead of a single simple feature such as an edge, CFR uses a large set of complex features that are learned from experience with model objects. The response of a single complex feature contains much more class information than does a single edge. This significantly reduces the number of possible correspondences between the model and the image. In addition, CFR takes advantage of a type of image processing called 'oriented energy'. Oriented energy is used to efficiently pre-process the image to eliminate some of the difficulties associated with changes in lighting and pose.

A Security Kernel Based on the Lambda-Calculus

Rees, Jonathan A.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 20 p.; 286190 bytes; 519667 bytes; application/postscript; application/pdf
Português
Cooperation between independent agents depends upon establishing adegree of security. Each of the cooperating agents needs assurance that the cooperation will not endanger resources of value to that agent. In a computer system, a computational mechanism can assure safe cooperation among the system's users by mediating resource access according to desired security policy. Such a mechanism, which is called a security kernel, lies at the heart of many operating systems and programming environments.The report describes Scheme 48, a programming environment whose design is guided by established principles of operating system security. Scheme 48's security kernel is small, consisting of the call-by-value $lambda$-calculus with a few simple extensions to support abstract data types, object mutation, and access to hardware resources. Each agent (user or subsystem) has a separate evaluation environment that holds objects representing privileges granted to that agent. Because environments ultimately determine availability of object references, protection and sharing can be controlled largely by the way in which environments are constructed. I will describe experience with Scheme 48 that shows how it serves as a robust and flexible experimental platform. Two successful applications of Scheme 48 are the programming environment for the Cornell mobile robots...

A Simplified Method for Deriving Equations of Motion For Continuous Systems with Flexible Members

Singer, Neil C.; Seering, Warren P.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 11 p.; 700835 bytes; 413499 bytes; application/octet-stream; application/pdf
Português
A method is proposed for deriving dynamical equations for systems with both rigid and flexible components. During the derivation, each flexible component of the system is represented by a "surrogate element" which captures the response characteristics of that component and is easy to mathematically manipulate. The derivation proceeds essentially as if each surrogate element were a rigid body. Application of an extended form of Lagrange's equation yields a set of simultaneous differential equations which can then be transformed to be the exact, partial differential equations for the original flexible system. This method's use facilitates equation generation either by an analyst or through application of software-based symbolic manipulation.

Space Efficient 3D Model Indexing

Jacobs, David W.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 23 p.; 2278295 bytes; 1790124 bytes; application/postscript; application/pdf
Português
We show that we can optimally represent the set of 2D images produced by the point features of a rigid 3D model as two lines in two high-dimensional spaces. We then decribe a working recognition system in which we represent these spaces discretely in a hash table. We can access this table at run time to find all the groups of model features that could match a group of image features, accounting for the effects of sensing error. We also use this representation of a model's images to demonstrate significant new limitations of two other approaches to recognition: invariants, and non- accidental properties.

A Novel Approach to Graphics

Poggio, Tomaso; Brunelli, Roberto
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 15 p.; 1356111 bytes; 1055073 bytes; application/postscript; application/pdf
Português
sWe show that we can optimally represent the set of 2D images producedsby the point features of a rigid 3D model as two lines in twoshigh-dimensional spaces. We then decribe a working recognition systemsin which we represent these spaces discretely in a hash table. We cansaccess this table at run time to find all the groups of model featuressthat could match a group of image features, accounting for the effectssof sensing error. We also use this representation of a model's imagessto demonstrate significant new limitations of two other approaches tosrecognition: invariants, and non-accidental properties.

Time-Reversible Maxwell's Demon

Skordos, P. A.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 37 p.; 1484265 bytes; 1170116 bytes; application/postscript; application/pdf
Português
A time-reversible Maxwell's demon is demonstrated which creates a density difference between two chambers initialized to have equal density. The density difference is estimated theoretically and confirmed by computer simulations. It is found that the reversible Maxwell's demon compresses phase space volume even though its dynamics are time reversible. The significance of phase space volume compression in operating a microscopic heat engine is also discussed.

Recognition and Structure from One 2D Model View: Observations on Prototypes, Object Classes and Symmetries

Poggio, Tomaso; Vetter, Thomas
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 22 p.; 1962838 bytes; 1538757 bytes; application/postscript; application/pdf
Português
In this note we discuss how recognition can be achieved from a single 2D model view exploiting prior knowledge of an object's structure (e.g. symmetry). We prove that for any bilaterally symmetric 3D object one non- accidental 2D model view is sufficient for recognition. Symmetries of higher order allow the recovery of structure from one 2D view. Linear transformations can be learned exactly from a small set of examples in the case of "linear object classes" and used to produce new views of an object from a single view.

Natural Language Based Inference Procedures Applied to Schubert's Steamroller

Givan, Robert; McAllester, David; Shalaby, Sameer
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 12 p.; 1093860 bytes; 853931 bytes; application/postscript; application/pdf
Português
We have previously argued that the syntactic structure of natural language can be exploited to construct powerful polynomial time inference procedures. This paper supports the earlier arguments by demonstrating that a natural language based polynomial time procedure can solve Schubert's steamroller in a single step.

The Supercomputer Toolkit: A General Framework for Special-purpose Computing

Abelson, Harold; Berlin, Andrew A.; Katzenelson, Jacob; McAllister, William H.; Rozas, Guillermo J.; Sussman, Gerald Jay; Wisdom, Jack
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 40 p.; 2949624 bytes; 2312975 bytes; application/postscript; application/pdf
Português
The Toolkit is a family of hardware modules (processors, memory, interconnect, and input-output devices) and a collection of software modules (compilers, simulators, scientific libraries, and high-level front ends) from which high-performance special-purpose computers can be easily configured and programmed. The hardware modules are intended to be standard, reusable parts. These are combined by means of a user- reconfigurable, static interconnect technology. T he Toolkit's software support, based on n ovel compilation techniques, produces e xtremely high- performance numerical code from high-level language input, and will eventually automatically configure hardware modules for particular applications.

A Control Algorithm for Chaotic Physical Systems

Bradley, Elizabeth
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 15 p.; 1289369 bytes; 1008469 bytes; application/postscript; application/pdf
Português
Control algorithms which exploit the unique properties of chaos can vastly improve the design and performance of many practical and useful systems. The program Perfect Moment is built around such an algorithm. Given two points in the system's state space, it autonomously maps the space, chooses a set of trajectory segments from the maps, uses them to construct a composite path between the points, then causes the system to follow that path. This program is illustrated with two practical examples: the driven single pendulum and its electronic analog, the phase-locked loop. Strange attractor bridges, which alter the reachability of different state space points, can be used to increase the capture range of the circuit.

Apparent Opacity Affects Perception of Structure from Motion

Kersten, Daniel; Bulthoff, Heinrich
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 14 p.; 3439426 bytes; 2734719 bytes; application/postscript; application/pdf
Português
The judgment of surface attributes such as transparency or opacity is often considered to be a higher-level visual process that would make use of low-level stereo or motion information to tease apart the transparent from the opaque parts. In this study, we describe a new illusion and some results that question the above view by showing that depth from transparency and opacity can override the rigidity bias in perceiving depth from motion. This provides support for the idea that the brain's computation of the surface material attribute of transparency may have to be done either before, or in parallel with the computation of structure from motion.

Control Algorithms for Chaotic Systems

Bradley, Elizabeth
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 21 p.; 3522928 bytes; 1357363 bytes; application/postscript; application/pdf
Português
This paper presents techniques that actively exploit chaotic behavior to accomplish otherwise-impossible control tasks. The state space is mapped by numerical integration at different system parameter values and trajectory segments from several of these maps are automatically combined into a path between the desired system states. A fine-grained search and high computational accuracy are required to locate appropriate trajectory segments, piece them together and cause the system to follow this composite path. The sensitivity of a chaotic system's state-space topology to the parameters of its equations and of its trajectories to the initial conditions make this approach rewarding in spite of its computational demands.

Solar energy and conservation at St. Mark’s School

Jones, William J.; Meyer, James W.
Fonte: MIT Energy Laboratory Publicador: MIT Energy Laboratory
Tipo: Relatório Formato: 14579592 bytes; application/pdf
Português
This report is a result of a request to investigate the possibility of employing solar energy at a residential secondary school to reduce energy costs. Our approach was to explore this possibility in the context of a more general survey of opportunities to conserve energy (in particular, fuel)at the school. Our purpose was more to illustrate how to go about an appraisal of conservation opportunities plus implementation and evaluation of the most productive conservation measures, than a rigorous examination of the facility with detailed instructions on how to take care of specific problems. A large number of actions that would result in net energy cost savings considerably greater than could be realized from solar systems were discovered. For a solar application, a domestic hot water system,supplementing that heated bytankless coils in oil burning furnaces,has the greatest potential for significant return on investment. The school's total utility system (total energy, co-generation) meets all electrical and steam needs with the exception of the electric power required for one building. A heat recovery system on the diesel engines for the electric generators furnishes a sizeable portion of the steam. Areas discussed in detail are: (1) optimization of the efficiency of oil fueled residential heating furnaces; (2) optimized operation of a total energy system; (3) lighting...

On Using First-Order Theorem Provers in the Jahob Data Structure Verification System

Bouillaguet, Charles; Kuncak, Viktor; Wies, Thomas; Zee, Karen; Rinard, Martin
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 32 p.; 397902 bytes; 1759318 bytes; application/pdf; application/postscript
Português
This paper presents our integration of efficient resolution-based theorem provers into the Jahob data structure verification system. Our experimental results show that this approach enables Jahob to automatically verify the correctness of a range of complex dynamically instantiable data structures, including data structures such as hash tables and search trees, without the need for interactive theorem proving or techniques tailored to individual data structures. Our primary technical results include: (1) a translation from higher-order logic to first-order logic that enables the application of resolution-based theorem provers and (2) a proof that eliminating type (sort) information in formulas is both sound and complete, even in the presence of a generic equality operator. Our experimental results show that the elimination of type information dramatically decreases the time required to prove the resulting formulas. These techniques enabled us to verify complex correctness properties of Java programs such as a mutable set implemented as an imperative linked list, a finite map implemented as a functional ordered tree, a hash table with a mutable array, and a simple library system example that uses these container data structures. Our system verifies (in a matter of minutes) that data structure operations correctly update the finite map...

Amorphous Medium Language

Beal, Jacob
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 7 p.; 408752 bytes; 2548880 bytes; application/pdf; application/postscript
Português
Programming reliable behavior on a large mesh network composed of unreliable parts is difficult. Amorphous Medium Language addresses this problem by abstracting robustness and networking issues away from the programmer via language of geometric primitives and homeostasis maintenance.AML is designed to operate on a high diameter network composed of thousands to billions of nodes, and does not assume coordinate, naming, or routing services. Computational processes are distributed through geometric regions of the space approximated by the network and specify behavior in terms of homeostasis conditions and actions to betaken when homeostasis is violated.AML programs are compiled for local execution using previously developed amorphous computing primitives which provide robustness against ongoing failures and joins and localize the impact of changes in topology. I show some examples of how AML allows complex robust behavior to be expressed in simple programs and some preliminary results from simulation.

Market and Infrastructure Analysis of Future Air Cargo Demand in China

Jiang, H.; Ren, L.; Hansman, R. J.
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Relatório Formato: 852656 bytes; application/pdf
Português
This paper describes an analysis of future air cargo demand in China and its implications for system infrastructure. By extrapolating current trends and evaluating government policies, China is projected to achieve sustained economic development over the next 20 years. Based on this assumption, a forecast for future air cargo demand is made for the period through 2020 using econometric methods. The forecast projects air cargo traffic growth at 11.2% per annum, expanding more than seven fold by 2020 – resulting in an expected 27 million tonnes cargo throughput originating from Chinese airports. A baseline forecast for the cargo throughput at the major hubs and large airports in mainland China, Hong Kong and Taiwan is presented.; The authors would like to thank Mr. Boxue Wang at Aviation Industry Development Research Center of China for providing some 2002 CAAC data and R. Dixon Speas Fellowship for partially supporting the research.

Virtual Monotonic Counters and Count-Limited Objects using a TPM without a Trusted OS (Extended Version)

Sarmenta, Luis F. G.; van Dijk, Marten; O'Donnell, Charles W.; Rhodes, Jonathan; Devadas, Srinivas
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Formato: 18 p.; 430350 bytes; 694048 bytes; application/pdf; application/postscript
Português
A trusted monotonic counter is a valuable primitive thatenables a wide variety of highly scalable offlineand decentralized applications that would otherwise be prone to replay attacks, including offline payment, e-wallets, virtual trusted storage, and digital rights management (DRM).In this paper, we show how one can implement a very large number of virtual monotonic counters on an untrusted machine with a Trusted Platform Module (TPM) or similar device, without relying on a trusted OS. We first present a log-based scheme that can be implemented with the current version of the TPM (1.2) and used incertain applications.We then show how the addition of a few simple features tothe TPM makes it possible to implement a hash-tree-based schemethat not only offers improved performance and scalability compared to the log-based scheme, but also makes it possible to implement count-limited objects (or ``clobs'' for short) -- i.e., encrypted keys, data, and other objectsthat can only be used when an associated virtual monotonic counter is within a certain range.Such count-limited objects include n-time use keys, n-out-of-m data blobs,n-copy migratable objects, and other variants, which have many potential uses in digital rights management (DRM)...

MIT's CWSpace project: packaging metadata for archiving educational content in DSpace

Reilly, William; Wolfe, Robert; Smith, MacKenzie
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica Formato: 211350 bytes; application/pdf
Português
This paper describes work in progress on the research project CWSpace, sponsored by the MIT and Microsoft Research iCampus program, to investigate the metadata standards and protocols required to archive the course materials found in MIT’s OpenCourseWare (OCW) into MIT’s institutional repository DSpace. The project goal is “to harvest and digitally archive OCW learning objects, and make them available to learning management systems by using Web Services interfaces on top of DSpace.” The larger vision is one of complex digital objects (CDOs) successfully interoperating amongst MIT’s various learning management systems and learning object repositories, providing archival preservation and persistent identifiers for educational materials, as well as providing the means to richer shared discovery and dissemination mechanisms for those materials. The paper describes work to date on the analysis of the content packaging metadata standards METS (Metadata Encoding and Transmission Standard) and especially IMS-CP (IMS Global Learning Consortium, Content Packaging), and issues faced in the development and use of profiles, extensions, and external schema for these standards. Also addressed are the anticipated issues in the preparation of transformations from one standard to another...

Book Review of G.A. Cohen, "Marx's Theory of History, A Defence".

Cohen, Joshua
Fonte: The Journal of Philosophy Publicador: The Journal of Philosophy
Tipo: Artigo de Revista Científica Formato: 3753070 bytes; application/pdf
Português
book review