Showing papers by "University of California, San Diego published in 1988"
TL;DR: Back-propagation repeatedly adjusts the weights of the connections in the network so as to minimize a measure of the difference between the actual output vector of the net and the desired output vector, which helps to represent important features of the task domain.
Abstract: We describe a new learning procedure, back-propagation, for networks of neurone-like units. The procedure repeatedly adjusts the weights of the connections in the network so as to minimize a measure of the difference between the actual output vector of the net and the desired output vector. As a result of the weight adjustments, internal ‘hidden’ units which are not part of the input or output come to represent important features of the task domain, and the regularities in the task are captured by the interactions of these units. The ability to create useful new features distinguishes back-propagation from earlier, simpler methods such as the perceptron-convergence procedure1.
23,814 citations
TL;DR: In this paper, a stress-strain model for concrete subjected to uniaxial compressive loading and confined by transverse reinforcement is developed for concrete sections with either spiral or circular hoops, or rectangular hoops with or without supplementary cross ties.
Abstract: A stress‐strain model is developed for concrete subjected to uniaxial compressive loading and confined by transverse reinforcement. The concrete section may contain any general type of confining steel: either spiral or circular hoops; or rectangular hoops with or without supplementary cross ties. These cross ties can have either equal or unequal confining stresses along each of the transverse axes. A single equation is used for the stress‐strain equation. The model allows for cyclic loading and includes the effect of strain rate. The influence of various types of confinement is taken into account by defining an effective lateral confining stress, which is dependent on the configuration of the transverse and longitudinal reinforcement. An energy balance approach is used to predict the longitudinal compressive strain in the concrete corresponding to first fracture of the transverse reinforcement by equating the strain energy capacity of the transverse reinforcement to the strain energy stored in the concret...
6,261 citations
TL;DR: A two-dimensional condensed-matter lattice model is presented which exhibits a nonzero quantization of the Hall conductance in the absence of an external magnetic field, and exhibits the so-called "parity anomaly" of (2+1)-dimensional field theories.
Abstract: A two-dimensional condensed-matter lattice model is presented which exhibits a nonzero quantization of the Hall conductance ${\ensuremath{\sigma}}^{\mathrm{xy}}$ in the absence of an external magnetic field. Massless fermions without spectral doubling occur at critical values of the model parameters, and exhibit the so-called "parity anomaly" of (2+1)-dimensional field theories.
4,606 citations
TL;DR: In this paper, the authors consider the relationship between causation and co-integration, and suggest that if a pair of I(1) series are cointegrated, there must be causation in at least one direction.
2,917 citations
01 Jan 1988
TL;DR: A model of context effects in perception is applied to the perception of letters in various contexts and exhibits the perceptual advantage for letters in words over unrelated contexts and is consistent with the basic facts about the word advantage.
Abstract: A model of context effects in perception is applied to the perception of letters in various contexts. In the model, perception results from excitatory and inhibitory interactions of detectors for visual features, letters, and words. A visual input excites detectors for visual features in the display. These excite detectors for letters consistent with the active features. The letter detectors in turn excite detectors for consistent words. Active word detectors mutually inhibit each other and send feedback to the letter level, strengthening activation and hence perceptibility of their constituent letters. Computer simulation of the model exhibits the perceptual advantage for letters in words over unrelated contexts and is consistent with the basic facts about the word advantage. Most importantly, the model produces facilitation for letters in pronounceable pseudowords as well as words. Pseudowords activate detectors for words that are consistent with most of the active letters, and feedback from the activated words strengthens the activations of the letters in the pseudoword. The model thus accounts for apparently rule-governed performance without any actual rules.
1,534 citations
TL;DR: Results are consistent with a model for transformation by SV40 which, at least in part, involves T/p110-114 complex formation and the perturbation of Rb protein and/or T function.
1,466 citations
TL;DR: It has been concluded that the types and yields of damaged moieties produced in intracellular DNA by low LET ionizing radiation are consistent with the mechanisms of production that involve both OH radical attack and a direct ionization of the macromolecule.
Abstract: Publisher Summary This chapter provides a framework for understanding the way permanent heritable damage in cellular DNA results from exposure to ionizing radiation. If the processes that occur in the time between the initial radiation energy deposition and the formation of such damage can be described, then rationales can be developed for the modulation of radiation damage. For example, it may be possible to (1) devise a means of differentially modulating the amounts of radiation damage, for instance, in tumor versus normal tissue in radiotherapy, or (2) predict the effects of variations of several parameters on the biological consequences of a radiation dose. It has been concluded that the types and yields of damaged moieties produced in intracellular DNA by low LET ionizing radiation are consistent with the mechanisms of production that involve both OH radical attack and a direct ionization of the macromolecule. At the radiation-dose levels producing one lethal lesion per cell, the amounts of damage produced by ionizing radiation are several orders of magnitude lower than the amounts of damage required for equal kill by other agents. Individual damaged moieties are not biologically significant; they can easily be repaired using the undamaged DNA strand as a template. The lethal lesion produced in cellular DNA is a locally multiply damaged site.
1,401 citations
TL;DR: Fos is a trans-acting factor that is capable of stimulating gene expression not by direct binding to DNA but by interaction with the sequence-specific transcription factor AP-1, therefore recognition of specific cis-elements by AP- 1 is a prerequisite for Fos-mediated stimulation of gene expression.
1,269 citations
TL;DR: A neural network model, programmed using back-propagation learning, can decode spatial information from area la neurons and accounts for their observed response properties.
Abstract: Neurons in area 7a of the posterior parietal cortex of monkeys respond to both the retinal location of a visual stimulus and the position of the eyes and by combining these signals represent the spatial location of external objects. A neural network model, programmed using back-propagation learning, can decode this spatial information from area 7a neurons and accounts for their observed response properties.
1,192 citations
TL;DR: The unexpected findings in these subjects were higher brain weights and greater number of neurons as compared to age‐matched nursing home control subjects, which suggest people may have had incipient Alzheimer's disease but escaped loss of large neurons, or started with larger brains and more large neurons and thus might be said to have had a greater reserve.
Abstract: Postmortem examination was performed on 137 residents (average age 85.5 years) of a skilled nursing facility whose mental status, memory, and functional status had been evaluated during life. Seventy-eight percent were demented using conservative criteria; 55% had characteristic Alzheimer's disease. Choline acetyltransferase and somatostatin were significantly reduced in the brains of patients with Alzheimer's disease as compared with age-matched nursing home control subjects, although the degree of the reduction was less severe than found in subjects less than 80 years of age. Ten subjects whose functional and cognitive performance was in the upper quintile of the nursing home residents, as good as or better than the performance of the upper quintile of residents without brain pathology (control subjects), showed the pathological features of mild Alzheimer's disease, with many neocortical plaques. Plaque counts were 80% of those of demented patients with Alzheimer's disease. Choline acetyltransferase and somatostatin levels were intermediate between controls and demented patients with Alzheimer's disease. The unexpected findings in these subjects were higher brain weights and greater number of neurons (greater than 90 micron 2 in a cross-sectional area in cerebral cortex) as compared to age-matched nursing home control subjects. These people may have had incipient Alzheimer's disease but escaped loss of large neurons, or alternatively, started with larger brains and more large neurons and thus might be said to have had a greater reserve.
1,163 citations
TL;DR: In this paper, the human transcription factor Jun/AP-1 was found to be responsible for increased transcription of different cellular genes in response to tumor promoters, such as TPA, and serum factors.
TL;DR: It is suggested that the NB system may serve as a structural basis for the concept of the generalized ascending activation of Moruzzi and Magoun (1949) by directly activating the neocortex and by suppressing the rhythm generation in the RT-thalamocortical circuitry.
Abstract: EEG and single-unit techniques have been used to study the EEG correlates of cellular firing in the neocortex, n. reticularis (RT) and “specific” thalamic nuclei, and the cholinergic forebrain area (nucleus basalis, NB). Neuronal firing was related to the ongoing behavior of the rat. In addition, using a 16-channel neocortical recording/mapping system, we studied the effects of ibotenic acid lesion of NB, RT, and other thalamic nuclei on the patterns and spatial distribution of neocortical electrical activity. The majority of neurons in neocortex, NB, and RT increased their firing rates during walking, as compared to during immobility, with concurrent decrease of delta power in the neocortical EEG. During immobility, high-voltage spindles (HVS; greater than 1 mV) were occasionally recorded from the neocortex. Depth profiles of HVS and slow delta waves were different in the neocortex. Neocortical cells decreased their discharge frequency during the positive portion of delta waves recorded in layers V and VI. All cells in the neocortex and specific thalamic nuclei fired rhythmically and phase-locked to the spike component of HVS. RT neurons showed an opposite phase relationship and fired mainly during the wave component of HVS. Half of the NB neurons also showed phasic modulation with HVS. Circumscribed lesion of RT and extensive damage of other thalamic regions, including the intralaminar nuclei, suppressed HVS but had no effect on the neocortical EEG correlates of behavior. In sharp contrast, damage to the NB resulted in a dramatic increase of slow delta waves on the side of the lesion, mimicking the effect of scopolamine administration. We suggest that the NB plays a key role in neocortical arousal by directly activating the neocortex and by suppressing the rhythm generation in the RT-thalamocortical circuitry. We further suggest that the NB system may serve as a structural basis for the concept of the generalized ascending activation of Moruzzi and Magoun (1949).
TL;DR: For instance, this article found that the detection of change when one display of familiar objects replaces another display might be based purely upon visual codes, or also on identity information (i.e., knowing what was present where in the initial display).
Abstract: Detection of change when one display of familiar objects replaces another display might be based purely upon visual codes, or also on identity information (i.e., knowingwhat was presentwhere in the initial display). Displays of 10 alphanumeric characters were presented and, after a brief offset, were presented again in the same position, with or without a change in a single character. Subjects’ accuracy in change detection did not suggest preservation of any more information than is usually available in whole report, except with the briefest of offsets (under 50 msec). Stimulus duration had only modest effects. The interaction of masking with offset duration followed the pattern previously observed with unfamiliar visual stimuli (Phillips, 1974). Accuracy was not reduced by reflection of the characters about a horizontal axis, suggesting that categorical information contributed negligibly. Detection of change appears to depend upon capacity-limited visual memory; (putative) knowledge of what identities are present in different display locations does not seem to contribute.
TL;DR: The nature of Vxc and the self-energy in real space is discussed, features and trends found in Si, GaAs, AlAs, and diamond are investigated, and the relationship of the calculated Vxc to the LDA and its extensions is examined.
Abstract: We show how the density-functional theory (DFT) exchange-correlation potential ${V}_{\mathrm{xc}(\mathrm{r}}$) of a semiconductor is calculated from the self-energy operator \ensuremath{\Sigma}(r,r',\ensuremath{\omega}), and how \ensuremath{\Sigma} is obtained using the one-particle Green's function and the screened Coulomb interaction (the GW approximation). We discuss the nature of ${V}_{\mathrm{xc}}$ and the self-energy in real space, and investigate features and trends found in Si, GaAs, AlAs, and diamond. In each case the calculated quasiparticle band structure is in good agreement with experiment, while the DFT band structure is surprisingly similar to that with the common local-density approximation (LDA); in particular, about 80% of the severe LDA band-gap error is shown to be inherent in DFT calculations, being accounted for by the discontinuity \ensuremath{\Delta} in ${V}_{\mathrm{xc}}$ upon addition of an electron. The relationship of the calculated ${V}_{\mathrm{xc}}$ to the LDA and its extensions is also examined.
TL;DR: The structure of Pit-1 and its recognition elements suggests that metazoan tissue phenotype is controlled by a family of transcription factors that bind to related cis-active elements and contain several highly conserved domains.
TL;DR: Using the DNA-binding domain of the human oestrogen receptor cDNA as a hybridization probe, two cDNA clones encoding polypeptides with structural features suggestive of cryptic steroid hormone receptors which could participate in a new hormone response system are isolated.
Abstract: The gonads and adrenal glands produce steroids classified into five major groups which include the oestrogens, progestins, androgens, glucocorticoids and mineralocorticoids. Gonadal steroids control the differentiation and growth of the reproductive system, induce and maintain sexual characteristics and modulate reproductive behaviour. Adrenal steroids also influence differentiation as well as being metabolic regulators. The effects of each steroid depend primarily on its specific receptors, the nature of which could therefore provide a basis for classification of steroid hormone action. The successful cloning, sequencing and expression of the human glucocorticoid (hGR) (ref. 1), oestrogen (hER), progesterone (hPR), and mineralocorticoid (hMR) receptors, complementary DNA, plus homologues from various species, provides the first opportunity to study receptor structure and its influence on gene expression. Sequence comparison and mutational analysis show structural features common to all groups of steroid hormone receptors. The receptors share a highly conserved cysteine-rich region which functions as the DNA-binding domain. This common segment allows the genome to be scanned for related gene products: hMR cDNA for example, was isolated using an hGR hybridization probe. In this study, using the DNA-binding domain of the human oestrogen receptor cDNA as a hybridization probe, we have isolated two cDNA clones encoding polypeptides with structural features suggestive of cryptic steroid hormone receptors which could participate in a new hormone response system.
TL;DR: The experimental results reported here indicate that the JUN oncoprotein is a sequence-specific transcriptional activator similar to AP-1, the product of the c-jun proto-oncogene.
Abstract: Proto-oncogenes encode proteins with three main sites of action: the cell-surface membrane, the cytoplasm and the nucleus. Although the exact biochemical function of most proto-oncogene products is not understood, several of them are known to be involved in signal transduction. A role in gene regulation through DNA binding has been suggested for a recently isolated member of the group of oncogenes acting at the nucleus, v-jun. The C-terminus of the putative v-jun-encoded protein is similar in sequence to the C-terminus of the yeast transcriptional activator GCN4 (refs 8, 9), which forms its minimal DNA-binding domain. GCN4 binds to specific sites whose consensus sequence is highly similar to the recognition sequence of the mammalian transcriptional activator AP-1 (refs 12, 13). Like GCN4, AP-1 binds to promoter elements of specific genes and activates their transcription. Because of the similarity between the recognition sites for GCN4 and AP-1, we examined the possibility that AP-1 could be the product of the c-jun proto-oncogene. The experimental results reported here indicate that the JUN oncoprotein is a sequence-specific transcriptional activator similar to AP-1.
TL;DR: This demonstration of suppression of the neoplastic phenotype by a single gene provides direct evidence for an essential role of the RB gene in tumorigenesis.
Abstract: Mutational inactivation of the retinoblastoma susceptibility (RB) gene has been proposed as a crucial step in the formation of retinoblastoma and other types of human cancer. This hypothesis was tested by introducing, via retroviral-mediated gene transfer, a cloned RB gene into retinoblastoma or osteosarcoma cells that had inactivated endogenous RB genes. Expression of the exogenous RB gene affected cell morphology, growth rate, soft agar colony formation, and tumorigenicity in nude mice. This demonstration of suppression of the neoplastic phenotype by a single gene provides direct evidence for an essential role of the RB gene in tumorigenesis.
TL;DR: It is shown that the yeast suc1 gene product (p13) is a potent inhibitor of MPF in cell-free extracts from Xenopus eggs and appears to exert its antagonistic effect by binding directly to MPF.
TL;DR: In this article, free-living bacteria, rather than the particle-feeding zooplankton, are the principal mediators of particle decomposition in the central north Pacific gyre and the eutrophic Santa Monica basin.
Abstract: Spatial and temporal patterns in the flux of sinking organic matter are central to the understanding of elemental dynamics and food-web energetics in the global ocean1–3. Heterotrophic bacteria have been shown to play a part in the decomposition of large, rapidly sinking organic particles within and below the euphotic zone4–8. These previous studies suggest that decomposition by attached bacteria can explain only a trivial fraction of the observed decrease in the flux of organic matter with increasing depth. We report here that free-living bacteria, rather than the particle-feeding zooplankton, are the principal mediators of particle decomposition in the central north Pacific gyre and the eutrophic Santa Monica basin. We suggest that bacterial growth in the mesopelagial gives rise to the large-scale production of fine (0.3–0.6 μm), non-sinking particles at the expense of large, rapidly sinking particles. Our results have implications for models of biogeochemical dynamics of organic particles and surface-reactive materials such as radionu-clides in the ocean's interior3,9.
TL;DR: The isolation of bovine and rat GHF-1 cDNA clones is described and it is indicated that this region of the protein functions as its DNA binding domain, which correlates with the selective transcription of its target, the GH gene.
TL;DR: A 30 amino acid peptide that functions as an activation domain has been localized in the carboxyl terminus of the human glucocorticoid receptor and may have certain properties in common with yeast activator sequences.
TL;DR: The results suggest that each of the three brainstem noradrenergic cell groups that contribute to the innervation of the PVH and/or the SO is in a position to modulate the activity of anatomically and chemically distinct groups of neurosecretory neurons.
Abstract: The distribution of neural inputs to the paraventricular (PVH) and supraoptic (SO) nuclei from the regions of the A1, the A2, and the A6 (locus coeruleus) noradrenergic cell groups was investigated by using a plant lectin, Phaseolus vulgaris leucoagglutinin (PHA-L), as an anterogradely transported tracer An immunofluorescence double-labeling procedure was used to determine the extent to which individual anterogradely labeled fibers and terminals in the PVH and the SO also displayed immunoreactive dopamine-beta-hydroxylase (DBH), a marker for catecholaminergic neurons The results may be summarized as follows: (1) Projections from the A1 region were found primarily, and in some experiments almost exclusively, in those parts of the magnocellular division of the PVH and the SO known to contain vasopressinergic neurons (2) Projections from the A2 region were distributed primarily throughout the parvicellular division of the PVH and were most dense in the dorsal medial part, a region known to contain a prominent population of corticotropin-releasing factor (CRF)-immunoreactive neurons In addition, a less-dense projection to the magnocellular division of the PVH and to the SO was consistently found (3) Fibers originating from the locus coeruleus were distributed almost exclusively to the parvicellular division of the PVH, with the most prominent input localized to the periventricular zone, a part of the PVH known to contain dopamine-, somatostatin-, and thyrotropin-releasing-hormone-containing neurons We found no evidence for a projection from A6 to the SO (4) The majority of fibers originating from the A1, the A2 or the A6 regions contained DBH immunoreactivity, although an appreciable number did not These results suggest that each of the three brainstem noradrenergic cell groups that contribute to the innervation of the PVH and/or the SO is in a position to modulate the activity of anatomically and chemically distinct groups of neurosecretory neurons
TL;DR: In this article, a set of Jastrow wave functions comprises exact eigenstates of a family of S = 1/2$ antiferromagnetic chains with exchange, and the full set of energy levels of this model is obtained; the spectrum exhibits remarkable ''supermultiplet'' degeneracies suggesting the existence of a hidden continuous symmetry.
Abstract: A set of Jastrow wave functions comprises exact eigenstates of a family of S= $\frac{1}{2}$ antiferromagnetic chains with ${\mathrm{r}}^{\mathrm{\ensuremath{-}}2}$ exchange. The ground state of the isotropic model is in this set, and is identical to the U\ensuremath{\rightarrow}\ensuremath{\infty} limit of the Gutzwiller wave function, also identified as Anderson's ``resonating-valence-bond'' state. The full set of energy levels of this model is obtained; the spectrum exhibits remarkable ``supermultiplet'' degeneracies suggesting the existence of a hidden continuous symmetry.
TL;DR: In this paper, the human visual system can rapidly and accurately derive the three-dimensional orientation of surfaces by using variations in image intensity alone, which is one of the most important yet poorly understood aspects of human vision.
Abstract: The human visual system can rapidly and accurately derive the three-dimensional orientation of surfaces by using variations in image intensity alone. This ability to perceive shape from shading is one of the most important yet poorly understood aspects of human vision. Here we present several findings which may help reveal computational mechanisms underlying this ability. First, we find that perception of shape from shading is a global operation which assumes that there is only one light source illuminating the entire visual image. This implies that if two identical objects are viewed simultaneously and illuminated from different angles, then we would be able to perceive three-dimensional shape accurately in only one of them at a time. Second, three-dimensional shapes that are defined exclusively by shading can provide tokens for the perception of apparent motion, suggesting that the motion mechanism is remarkably versatile in the kinds of inputs it can use. Lastly, the occluding edges which delineate an object from its background can also powerfully influence the perception of three-dimensional shape from shading.
TL;DR: The distribution of native, chaparral-requiring bird species was determined for 37 isolated fragments of canyon habitat ranging in size from 0.4 to 104 hectares in coasta4 urban San Diego County, California as mentioned in this paper.
Abstract: The distribution of native, chaparral-requiring bird species was determined for 37 isolated fragments of canyon habitat ranging in size from 0.4 to 104 hectares in coasta4 urban San Diego County, California The area of chaparral habitat and canyon age (time since isolation of the habitat fragment) explains most of the variation in the number of chaparral-requiring bird species. In additiolz, the distribution of native predators may influence species num- ber. There is statistical evidence that coyotes control thepop- ulations of smallerpredators such as foxes and domestic cats. The absence of coyotes may lead to higher levels of predation by a process of mesopredator release. The distance of canyons from otherpatches of chaparral habitat does not add significantly to the explained variance in chaparral- requiring species number-probably because of the virtual inability of most chaparral-requiring species to disperse through developed areas and nonscrub habitats. These re- sults and other lines of evidence suggest that chaparral- requiring birds in isolated canyons have very high rates of extinction, in part because of their low vagility. The best predictors of vulnerability of the individual species are their abundances (densities) in undisturbed habitat and their
TL;DR: Comparisons of cDNAs encoding potential finger proteins indicate the existence of at least two classes of proteins with specific nucleic acid recognition capabilities, characterized according to the number and position of the cysteine and histidine residues available for zinc coordination.
TL;DR: For des fonctions positives u and v, on considere le systeme D 1 Δu-χ⊇•(u⊆logv)=0, D 2 Δv-av+bu=0 dans Ω; ∂u/∂n=∂v/οn=0 sur ∂Ω, |Ω| −1 ∫ Ω u(x)dx=ū, ou |Φ| est le volume de Ω et ū>0 est une constante don
TL;DR: A dementia screening survey was carried out in Shanghai using a culturally adapted Chinese version of the Mini-Mental State Examination, with a significant increase in low scores on the mental status test and a different error pattern, reflecting the lack of formal education.
24 Jul 1988
TL;DR: Having to deal with the salient features of economic data highlights the role to be played by statistical inference and requires modifications to standard learning techniques which may prove useful in other contexts.
Abstract: A report is presented of some results of an ongoing project using neural-network modeling and learning techniques to search for and decode nonlinear regularities in asset price movements. The author focuses on the case of IBM common stock daily returns. Having to deal with the salient features of economic data highlights the role to be played by statistical inference and requires modifications to standard learning techniques which may prove useful in other contexts. >