Showing papers by "Massachusetts Institute of Technology published in 1992"
10,063 citations
TL;DR: In this article, the authors describe recent technical developments that have made the total-energy pseudopotential the most powerful ab initio quantum-mechanical modeling method presently available, and they aim to heighten awareness of the capabilities of the method in order to stimulate its application to as wide a range of problems in as many scientific disciplines as possible.
Abstract: This article describes recent technical developments that have made the total-energy pseudopotential the most powerful ab initio quantum-mechanical modeling method presently available. In addition to presenting technical details of the pseudopotential method, the article aims to heighten awareness of the capabilities of the method in order to stimulate its application to as wide a range of problems in as many scientific disciplines as possible.
7,666 citations
16 Nov 1992
TL;DR: Optical coherence tomography (OCT) has developed rapidly since its first realisation in medicine and is currently an emerging technology in the diagnosis of skin disease as mentioned in this paper, where OCT is an interferometric technique that detects reflected and backscattered light from tissue.
Abstract: Optical coherence tomography (OCT) has developed rapidly since its first realisation in medicine and is currently an emerging technology in the diagnosis of skin disease. OCT is an interferometric technique that detects reflected and backscattered light from tissue and is often described as the optical analogue to ultrasound. The inherent safety of the technology allows for in vivo use of OCT in patients. The main strength of OCT is the depth resolution. In dermatology, most OCT research has turned on non-melanoma skin cancer (NMSC) and non-invasive monitoring of morphological changes in a number of skin diseases based on pattern recognition, and studies have found good agreement between OCT images and histopathological architecture. OCT has shown high accuracy in distinguishing lesions from normal skin, which is of great importance in identifying tumour borders or residual neoplastic tissue after therapy. The OCT images provide an advantageous combination of resolution and penetration depth, but specific studies of diagnostic sensitivity and specificity in dermatology are sparse. In order to improve OCT image quality and expand the potential of OCT, technical developments are necessary. It is suggested that the technology will be of particular interest to the routine follow-up of patients undergoing non-invasive therapy of malignant or premalignant keratinocyte tumours. It is speculated that the continued technological development can propel the method to a greater level of dermatological use.
6,095 citations
TL;DR: Results indicate that while a 3-fold reduction in levels of genomic m5C has no detectable effect on the viability or proliferation of ES cells in culture, a similar reduction of DNA methylation in embryos causes abnormal development and embryonic lethality.
3,994 citations
15 Aug 1992
TL;DR: As part of a series of evaluated sets, rate constants and photochemical cross sections compiled by the NASA Panel for Data Evaluation are provided in this article, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena.
Abstract: As part of a series of evaluated sets, rate constants and photochemical cross sections compiled by the NASA Panel for Data Evaluation are provided. The primary application of the data is in the modeling of stratospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena. Copies of this evaluation are available from the Jet Propulsion Laboratory.
3,218 citations
TL;DR: Three participants are identified (AT gene(s), p53, and GADD45) in a signal transduction pathway that controls cell cycle arrest following DNA damage; abnormalities in this pathway probably contribute to tumor development.
3,098 citations
TL;DR: This paper shows, by means of an operator called asplitting operator, that the Douglas—Rachford splitting method for finding a zero of the sum of two monotone operators is a special case of the proximal point algorithm, which allows the unification and generalization of a variety of convex programming algorithms.
Abstract: This paper shows, by means of an operator called asplitting operator, that the Douglas--Rachford splitting method for finding a zero of the sum of two monotone operators is a special case of the proximal point algorithm. Therefore, applications of Douglas--Rachford splitting, such as the alternating direction method of multipliers for convex programming decomposition, are also special cases of the proximal point algorithm. This observation allows the unification and generalization of a variety of convex programming algorithms. By introducing a modified version of the proximal point algorithm, we derive a new,generalized alternating direction method of multipliers for convex programming. Advances of this sort illustrate the power and generality gained by adopting monotone operator theory as a conceptual framework.
2,913 citations
TL;DR: The introduction of a mutation in RAG-1 into the germline of mice via gene targeting in embryonic stem cells is described and it is shown that this mutation either activates or catalyzes the V(D)J recombination reaction of immunoglobulin and T cell receptor genes.
2,821 citations
TL;DR: Using positional cloning strategies, this work has identified a CTG triplet repeat that undergoes expansion in myotonic dystrophy patients and PCR analysis of the interval containing this repeat indicates that unaffected individuals have been 5 and 27 copies.
2,606 citations
TL;DR: In this paper, the electronic structure for graphenemonolayer tubules is predicted as a function of the diameter and helicity of the constituent graphene tubules, and it is shown that approximately 1/3 of these tubules are a one-dimensional metal which is stable against a Peierls distortion, and the other 2/3 are onedimensional semiconductors.
Abstract: The electronic structure for graphenemonolayer tubules is predicted as a function of the diameter and helicity of the constituent graphene tubules. The calculated results show that approximately 1/3 of these tubules are a one‐dimensional metal which is stable against a Peierls distortion, and the other 2/3 are one‐dimensional semiconductors. The implications of these results are discussed.
2,405 citations
TL;DR: A Landauer formula for the current through a region of interacting electrons is derived using the nonequilibrium Keldysh formalism, and an enhanced conductance is predicted for tunneling through a quantum dot in the fractional quantum Hall regime.
Abstract: A Landauer formula for the current through a region of interacting electrons is derived using the nonequilibrium Keldysh formalism. The case of proportionate coupling to the left and right leads, where the formula takes an especially simple form, is studied in more detail. Two particular examples where interactions give rise to novel effects in the current are discussed: In the Kondo regime, an enhanced conductance is predicted, while a suppressed conductance is predicted for tunneling through a quantum dot in the fractional quantum Hall regime.
TL;DR: A direct adaptive tracking control architecture is proposed and evaluated for a class of continuous-time nonlinear dynamic systems for which an explicit linear parameterization of the uncertainty in the dynamics is either unknown or impossible.
Abstract: A direct adaptive tracking control architecture is proposed and evaluated for a class of continuous-time nonlinear dynamic systems for which an explicit linear parameterization of the uncertainty in the dynamics is either unknown or impossible. The architecture uses a network of Gaussian radial basis functions to adaptively compensate for the plant nonlinearities. Under mild assumptions about the degree of smoothness exhibit by the nonlinear functions, the algorithm is proven to be globally stable, with tracking errors converging to a neighborhood of zero. A constructive procedure is detailed, which directly translates the assumed smoothness properties of the nonlinearities involved into a specification of the network required to represent the plant to a chosen degree of accuracy. A stable weight adjustment mechanism is determined using Lyapunov theory. The network construction and performance of the resulting controller are illustrated through simulations with example systems. >
TL;DR: Bailyn et al. as discussed by the authors used semistructured interviews with 38 new-product team managers in high-technotogy companies, log data from two of these teams, and questionnaires completed by members of a different set of AB newproduct teams to generate and test hypotheses about teams' external activities.
Abstract: We thank Lotte Bailyn, Keith Mumighan. Elaine RtMnanelli, the Center for Innovation Management Studies. Bob Sutton, and tfie anonymous reviewers at Administrative Science Quarteriy for their support and comments. This article focuses on the activities teams use to manage their organizational environment beyond their teams. We used semistructured interviews with 38 new-product team managers in high-technotogy companies, log data from two of these teams, and questionnaires completed by members of a different set of AB new-product teams to generate and test hypotheses about teams' external activities. Results indicate that teams engage in vertical communications aimed at molding the views of top management, horizontal communication aimed at coordinating work and obtaining feedback, and horizontal communication aimed at general scanning of the technical and market environment. Organizational teams appear to develop distinct strategies toward their environment: some specialize in particular external activities, some remain isolated from the extemal environment, and others engage in multiple external activities. The paper shows that the type of external communication teams engage in, not just the amount, determines performance. Over time, teams following a comprehensive strategy enter positive cycles of external activity, internal processes, and performance that enable long-term team success.*
TL;DR: The goal of the Laser Interferometer Gravitational-Wave Observatory (LIGO) Project is to detect and study astrophysical gravitational waves and use data from them for research in physics and astronomy.
Abstract: The goal of the Laser Interferometer Gravitational-Wave Observatory (LIGO) Project is to detect and study astrophysical gravitational waves and use data from them for research in physics and astronomy. LIGO will support studies concerning the nature and nonlinear dynamics of gravity, the structures of black holes, and the equation of state of nuclear matter. It will also measure the masses, birth rates, collisions, and distributions of black holes and neutron stars in the universe and probe the cores of supernovae and the very early universe. The technology for LIGO has been developed during the past 20 years. Construction will begin in 1992, and under the present schedule, LIGO's gravitational-wave searches will begin in 1998.
TL;DR: In this paper, the authors presented a new approach to remote sensing of water vapor based on the global positioning system (GPS) for estimating the extent to which signals propagating from GPS satellites to ground-based GPS receivers are delayed by atmospheric water vapor.
Abstract: We present a new approach to remote sensing of water vapor based on the global positioning system (GPS). Geodesists and geophysicists have devised methods for estimating the extent to which signals propagating from GPS satellites to ground-based GPS receivers are delayed by atmospheric water vapor. This delay is parameterized in terms of a time-varying zenith wet delay (ZWD) which is retrieved by stochastic filtering of the GPS data. Given surface temperature and pressure readings at the GPS receiver, the retrieved ZWD can be transformed with very little additional uncertainty into an estimate of the integrated water vapor (IWV) overlying that receiver. Networks of continuously operating GPS receivers are being constructed by geodesists, geophysicists, government and military agencies, and others in order to implement a wide range of positioning capabilities. These emerging GPS networks offer the possibility of observing the horizontal distribution of IWV or, equivalently, precipitable water with unprecedented coverage and a temporal resolution of the order of 10 min. These measurements could be utilized in operational weather forecasting and in fundamental research into atmospheric storm systems, the hydrologic cycle, atmospheric chemistry, and global climate change. Specially designed, dense GPS networks could be used to sense the vertical distribution of water vapor in their immediate vicinity. Data from ground-based GPS networks could be analyzed in concert with observations of GPS satellite occultations by GPS receivers in low Earth orbit to characterize the atmosphere at planetary scale.
TL;DR: In particular, tectonically driven increases in chemical weathering may have resulted in a decrease of atmospheric C02 concentration over the past 40 Myr as discussed by the authors. But this was not shown to be the case for the uplift of the Tibetan plateau and positive feedbacks initiated by this event.
Abstract: Global cooling in the Cenozoic, which led to the growth of large continental ice sheets in both hemispheres, may have been caused by the uplift of the Tibetan plateau and the positive feedbacks initiated by this event. In particular, tectonically driven increases in chemical weathering may have resulted in a decrease of atmospheric C02 concentration over the past 40 Myr.
TL;DR: This study of 6-month-old infants from two countries, the United States and Sweden, shows that exposure to a specific language in the first half year of life alters infants' phonetic perception.
Abstract: Linguistic experience affects phonetic perception. However, the critical period during which experience affects perception and the mechanism responsible for these effects are unknown. This study of 6-month-old infants from two countries, the United States and Sweden, shows that exposure to a specific language in the first half year of life alters infants' phonetic perception.
TL;DR: In this article, the authors investigated the impact of diversity on team performance and found that functional and tenure diversity each has its own distinct effects, and that the greater the functional diversity, the more team members communicated outside the team's boundaries.
Abstract: The increasing reliance on teams in organizations raises the question of how these teams should be formed. Should they be formed completely of engineers or should they include a range of specialists? Should they be made up to people who have long tenure in the organization, or those with a wide range of experience? As teams increasingly get called upon to do more complex tasks and to cross functional boundaries within the organization, conventional wisdom has suggested that teams be composed of more diverse members. This study suggests that the answer may not be so simple. Using 409 individuals from 45 new product teams in five high-technology companies, this study investigates the impact of diversity on team performance. We found that functional and tenure diversity each has its own distinct effects. The greater the functional diversity, the more team members communicated outside the team's boundaries. This communication was with a variety of groups such as marketing, manufacturing, and top management. T...
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12 Aug 1992TL;DR: Theory and models of supervisory control of teleoperators for space, undersea, and other applications are discussed in this paper, where the social implications of telerobotics, automation, and super-visory control are discussed.
Abstract: Theory and models of supervisory control - frameworks and fragments supervisory control of anthropomorphic teleoperators for space, undersea, and other applications supervisory control in transportation, process, and other automated systems social implications of telerobotics, automation, and supervisory control.
TL;DR: Results suggest that the demonstrated preferential transport of GSSG compared to GSH into the ER lumen may contribute to this redox compartmentation.
Abstract: The redox state of the endoplasmic reticulum (ER) was measured with the peptide N-Acetyl-Asn-Tyr-Thr-Cys-NH2. The peptide diffused across cellular membranes; some became glycosylated and thus trapped within the secretory pathway, and its cysteine residue underwent reversible thiol-disulfide exchanges with the surrounding redox buffer. Glycosylated peptides from cells were disulfide-linked to glutathione, indicating that glutathione is the major redox buffer in the secretory pathway. The redox state of the secretory pathway was more oxidative than that of the cytosol; the ratio of reduced glutathione to the disulfide form (GSH/GSSG) within the secretory pathway ranged from 1:1 to 3:1, whereas the overall cellular GSH/GSSG ratio ranged from 30:1 to 100:1. Cytosolic glutathione was also transported into the lumen of microsomes in a cell-free system. Although how the ER maintains an oxidative environment is not known, these results suggest that the demonstrated preferential transport of GSSG compared to GSH into the ER lumen may contribute to this redox compartmentation.
TL;DR: A mouse strain has been constructed in which one allele of Rb is disrupted, and heterozygous animals are not predisposed to retinoblastoma, but some display pituitary tumours arising from cells in which the wild-type Rb allele is absent.
Abstract: The retinoblastoma gene is mutated in several types of human cancer and is the best characterized of the tumour-suppressor genes. A mouse strain has been constructed in which one allele of Rb is disrupted. These heterozygous animals are not predisposed to retinoblastoma, but some display pituitary tumours arising from cells in which the wild-type Rb allele is absent. Embryos homozygous for the mutation die between days 14 and 15 of gestation, exhibiting neuronal cell death and defective erythropoiesis.
TL;DR: In this paper, a learnability paradox between argument structure and the lexicon is resolved by using argument structure as a pointer between syntactic structure and propositions, and the autonomy of semantic representation implications for the semantic bootstrapping hyposthesis conservatism, listedness and lexicon spatial schemas and abstract thought.
Abstract: Part 1 A learnability paradox: argument structure and the lexicon the logical problem of language acquisition Baker's paradox attempted solutions to Baker's paradox. Part 2 Constraints on lexical rules: morphological and phonological constraints semantic constraints how semantic and morphological constraints might resolve Baker's paradox evidence for criteria-governed productivity problems for the criteria-governed productivity theory. Part 3 Constraints and the nature of argument structure: overview - why lexical rules carry semantic constraints constraints of lexical rules as manifestations of more general phenomena a theory of argument structure on universality. Part 4 Possible and actual forms: the problem of negative exceptions transitive action verbs as evidence for narrow subclasses the nature of narrow conflation classes defining and motivating subclasses of verbs licensing the four alterations the relation between narrow-range and broad-range rules. Part 5 Representation: the need for a theory of lexicosemantic representation is a theory of lexical semantics feasible? evidence for a semantic subsystem underlying verb meanings a cross-linguistic inventory of components of verb meaning a theory of the representation of grammatically relevant semantic structures explicit representations of lexical rules an lexicosemantic structures summary. Part 6 Learning: linking rules lexical semantic structures broad conflation classes (thematic cores) and broad range lexical rules summary of learning mechanisms. Part 7 Development: developmental sequence for argument structure alterations the unlearning problem children's argument structure changing rules are always semantically conditioned do children's errors have the same cause as adults? acquisition of verb meaning and errors in argument structure some predictions about the acquisition of narrow-range rules summary of development. Part 8 Conclusions: a brief summary of the resolution of the paradox argument structure as a pointer between syntactic structure and propositions the autonomy of semantic representation implications for the semantic bootstrapping hyposthesis conservatism, listedness and the lexicon spatial schemas and abstract thought.
TL;DR: W Whole cell recordings reveal that postsynaptic mechanisms, including N-methyl-D-aspartate (NMDA) receptor function, are intact and are therefore a suitable model for studying the relation between LTP and learning processes.
Abstract: As a first step in a program to use genetically altered mice in the study of memory mechanisms, mutant mice were produced that do not express the alpha-calcium-calmodulin-dependent kinase II (alpha-CaMKII). The alpha-CaMKII is highly enriched in postsynaptic densities of hippocampus and neocortex and may be involved in the regulation of long-term potentiation (LTP). Such mutant mice exhibited mostly normal behaviors and presented no obvious neuroanatomical defects. Whole cell recordings reveal that postsynaptic mechanisms, including N-methyl-D-aspartate (NMDA) receptor function, are intact. Despite normal postsynaptic mechanisms, these mice are deficient in their ability to produce LTP and are therefore a suitable model for studying the relation between LTP and learning processes.
TL;DR: Two examples of jointly shiftable transforms that are simultaneously shiftable in more than one domain are explored and the usefulness of these image representations for scale-space analysis, stereo disparity measurement, and image enhancement is demonstrated.
Abstract: One of the major drawbacks of orthogonal wavelet transforms is their lack of translation invariance: the content of wavelet subbands is unstable under translations of the input signal. Wavelet transforms are also unstable with respect to dilations of the input signal and, in two dimensions, rotations of the input signal. The authors formalize these problems by defining a type of translation invariance called shiftability. In the spatial domain, shiftability corresponds to a lack of aliasing; thus, the conditions under which the property holds are specified by the sampling theorem. Shiftability may also be applied in the context of other domains, particularly orientation and scale. Jointly shiftable transforms that are simultaneously shiftable in more than one domain are explored. Two examples of jointly shiftable transforms are designed and implemented: a 1-D transform that is jointly shiftable in position and scale, and a 2-D transform that is jointly shiftable in position and orientation. The usefulness of these image representations for scale-space analysis, stereo disparity measurement, and image enhancement is demonstrated. >
TL;DR: Familiarity, ease of access, trust, and awareness of benefits and risks to minimize uncertainty, will all be important for the sustained support of existing and new generations of DNA-B isolaters.
Abstract: INTRODUCTION . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1054 FAMILIES OF DNA-B INDING PROTEINS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . , 1054 He lix-Tum-He lix . . ... . . . . . . .. . . . . . . . ..... . . . . . . . . . . . . ... . . . . . . . ... . . . . . .. . . . . . . . . . . . . . 1055 Hom eo doma in . 1062 Zin c Fin ger . . . . . . . . . . . .. . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . 1069 S teroid Rece ptor . . . . . .. . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . .. . . . . . . . . . 1073 Leu cine Zi pper and Heli x-Loo p-He li x 1074 (3-Sh eet M o tlfs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1077 Other Fam ilie s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1079 PRINCIPLES OF R ECOGNITION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1080 Helices in Reco gn ition . . .. . . . . ... . . . . ..... . . . . . . ... . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1080 In te raction s with Base s . . . . . . . . . . . . . . . . .. . . . . . . .. . . . .. . . . . . .... . . . . . . . ... . . . . . .. . . . . . . . . . .. . . . . . . 1081 Con ta cts with th e DNA Bac kbon e . . . ... . . . . . . ... . . . . . . . .. . . . . . ... . . . . . . . .. . . . . . . . . . . . . . . . . . . . . 1084 Ro le of DNA Struc tu re in Reco gn ition . . . . . . . . . . . . . . . . . . . . . . . ...... . . . . .... . . . . . ... . . ........ 1085 Gene ra l Prin ciple s of S ite-S pecific Recogn ition . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . .. . . . . . . . . 1087
TL;DR: An adaptive algorithm for radar target detection using an antenna array is proposed that contains a simplified test statistic that is a limiting case of the GLRT detector.
Abstract: An adaptive algorithm for radar target detection using an antenna array is proposed. The detector is derived in a manner similar to that of the generalized likelihood-ratio test (GLRT) but contains a simplified test statistic that is a limiting case of the GLRT detector. This simplified detector is analyzed for performance to signals on boresight, as well as when the signal direction is misaligned with the look direction. >
TL;DR: In this paper, the authors demonstrate that certain classical problems associated with the notion of the teacher in supervised learning can be solved by judicious use of learned internal models as components of the adaptive system.
TL;DR: In this article, the authors propose the notion of genres of organizational communication as a concept useful for studying communication as embedded in social process rather than as the result of isolated rational actions.
Abstract: Drawing on rhetorical theory and structuration, this article proposes genres of organizational communication as a concept useful for studying communication as embedded in social process rather than as the result of isolated rational actions. Genres (e.g. the memo, the proposal, and the meeting) are typified communicative actions characterized by similar substance and form and taken in response to recurrent situations. These genres evolve over time in reciprocal interaction between institutionalized practices and individual human actions. They are distinct from communication media, though media may play a role in genre form, and the introduction of new media may occasion genre evolution. After the genre concept is developed, the article shows how it addresses existing limitations in research on media, demonstrates its usefulness in an extended historical example, and draws implications for future research.
01 May 1992
TL;DR: The authors propose the use of a packet service discipline at the nodes of the network that is based on a multiplex scheme called generalized processor sharing (GPS) that is combined with leaky bucket rate admission control to provide flexible, efficient and fair use of the links.
Abstract: Worst-case bounds on delay and backlog are derived for leaky bucket constrained sessions in arbitrary topology networks of generalized processor sharing servers. When only a subset of the sessions are leaky bucket constrained succinct per-session bounds that are independent of the behavior of the other sessions and also of the network topology are given. However, these bounds are only shown to hold for each session that is guaranteed a backlog clearing rate that exceeds the token arrival rate of its leaky bucket. When all of the sessions are leaky bucket constrained, a much larger class of networks called consistent relative session treatment networks is analyzed. The session i route is treated as a whole, yielding tighter bounds than those that result from adding the worst-case delays (backlogs) at each of the servers in the route. The bounds on delay and backlog for each session are computed and shown to be achieved by staggered regimes when an independent sessions relaxation holds. Propagation delay is also incorporated into the model. >
TL;DR: The data considerably strengthen the contention that the synaptic changes exhibited in LTP are the basis for spatial memory.
Abstract: Although long-term potentiation (LTP) has been studied as the mechanism for hippocampus-dependent learning and memory, evidence for this hypothesis is still incomplete. The mice with a mutation in the alpha-calcium-calmodulin-dependent kinase II (alpha-CaMKII), a synaptic protein enriched in the hippocampus, are appropriate for addressing this issue because the hippocampus of these mice is deficient in LTP but maintains intact postsynaptic mechanisms. These mutant mice exhibit specific learning impairments, an indication that alpha-CaMKII has a prominent role in spatial learning, but that it is not essential for some types of non-spatial learning. The data considerably strengthen the contention that the synaptic changes exhibited in LTP are the basis for spatial memory.