Showing papers by "University of California, Davis published in 1996"
TL;DR: This biennial Review summarizes much of particle physics, using data from previous editions.
12,798 citations
TL;DR: It is shown that a learning algorithm that attempts to find sparse linear codes for natural scenes will develop a complete family of localized, oriented, bandpass receptive fields, similar to those found in the primary visual cortex.
Abstract: The receptive fields of simple cells in mammalian primary visual cortex can be characterized as being spatially localized, oriented and bandpass (selective to structure at different spatial scales), comparable to the basis functions of wavelet transforms. One approach to understanding such response properties of visual neurons has been to consider their relationship to the statistical structure of natural images in terms of efficient coding. Along these lines, a number of studies have attempted to train unsupervised learning algorithms on natural images in the hope of developing receptive fields with similar properties, but none has succeeded in producing a full set that spans the image space and contains all three of the above properties. Here we investigate the proposal that a coding strategy that maximizes sparseness is sufficient to account for these properties. We show that a learning algorithm that attempts to find sparse linear codes for natural scenes will develop a complete family of localized, oriented, bandpass receptive fields, similar to those found in the primary visual cortex. The resulting sparse image code provides a more efficient representation for later stages of processing because it possesses a higher degree of statistical independence among its outputs.
5,947 citations
TL;DR: It is concluded that trophic cascades and top-down community regulation as envisioned by trophIC-level theories are relatively uncommon in nature.
Abstract: Food webs in nature have multiple, reticulate connections between a diversity of consumers and resources. Such complexity affects web dynamics: it first spreads the direct effects of consumption and productivity throughout the web rather than focusing them at particular "trophic levels." Second, consumer densities are often donor controlled with food from across the trophic spectrum, the herbivore and detrital channels, other habitats, life-history omnivory, and even trophic mutualism. Although consumers usually do not affect these resources, increased numbers often allow consumers to depress other resources to levels lower than if donor-controlled resources were absent. We propose that such donor-controlled and "multichannel" omnivory is a general feature of consumer control and central to food web dynamics. This observation is contrary to the normal practice of inferring dynamics by simplifying webs into a few linear "trophic levels," as per "green world" theories. Such theories do not accommodate commo...
1,995 citations
TL;DR: The authors examined the impact of accounting-based performance measures on the test statistics designed to detect abnormal operating performance and found that commonly used research designs yield test statistics that are misspecified in cases where sample firms have performed either unusually well or poorly.
1,796 citations
Posted Content•
TL;DR: This paper found that outsourcing can account for 31-51% of the increase in the relative demand for skilled labor that occurred in US manufacturing industries during the 1980s, compared to their previous estimate of 15-33% by using data from the revised NBER trade database.
Abstract: There is considerable debate over whether international trade has contributed to the declining economic fortunes of less skilled workers One issue that has become lost in the current discussion is how firms respond to import competition and how these responses, in turn, are transmitted to the labor market In previous work, we have argued that outsourcing, by which we mean the import of intermediate inputs by domestic firms, has contributed to an increase in the relative demand for skilled labor in the United States If firms respond to import competition from low-wage countries by moving non- skill-intensive activities abroad, then trade will shift employment towards skilled workers within industries In this paper, we extend our previous work by combining new import data from the revised NBER trade database with disaggregated data on input purchases from the Census of Manufactures We construct industry-by-industry estimates of outsourcing for the period 1972-1990 and reexamine whether outsourcing has contributed to an increase in relative demand for skilled labor Our main finding is that outsourcing can account for 31-51% of the increase in the relative demand for skilled labor that occurred in US manufacturing industries during the 1980s, compared to our previous estimate of 15-33%
1,469 citations
TL;DR: This paper argued that compliance is generally quite good and that this high level of compliance has been achieved with little attention to enforcement, and that those compliance problems that do exist are best addressed as management rather than enforcement problems.
Abstract: Recent research on compliance in international regulatory regimes has argued (1) that compliance is generally quite good; (2) that this high level of compliance has been achieved with little attention to enforcement; (3) that those compliance problems that do exist are best addressed as management rather than enforcement problems; and (4) that the management rather than the enforcement approach holds the key to the evolution of future regulatory cooperation in the international system. While the descriptive findings above are largely correct, the policy inferences are dangerously contaminated by endogeneity and selection problems. A high rate of compliance is often the result of states formulating treaties that require them to do little more than they would do in the absence of a treaty. In those cases where noncompliance does occur and where the effects of selection are attenuated, both self-interest and enforcement play significant roles.
1,285 citations
TL;DR: It was found that ARPE-19 cells exhibit morphological polarization when plated on laminin-coated Transwell-COL filters in medium with a low serum content and has structural and functional properties characteristic of RPE cells in vivo, suggesting that this cell line will be valuable for in vitro studies of retinal pigment epithelium physiology.
1,269 citations
TL;DR: In this article, the authors studied the probability that a setJ consisting of a finite union of intervals contains no eigenvalues for the finite N Gaussian Orthogonal (β = 1) and Gaussian Symplectic (β= 4) ensembles and their respective scaling limits both in the bulk and at the edge of the spectrum.
Abstract: The focus of this paper is on the probability,Eβ(O;J), that a setJ consisting of a finite union of intervals contains no eigenvalues for the finiteN Gaussian Orthogonal (β=1) and Gaussian Symplectic (β=4) Ensembles and their respective scaling limits both in the bulk and at the edge of the spectrum. We show how these probabilities can be expressed in terms of quantities arising in the corresponding unitary (β=2) ensembles. Our most explicit new results concern the distribution of the largest eigenvalue in each of these ensembles. In the edge scaling limit we show that these largest eigenvalue distributions are given in terms of a particular Painleve II function.
1,083 citations
12 May 1996
TL;DR: An RSA-based signing scheme which combines essentially optimal efficiency with attractive security properties and a second scheme which maintains all of the above features and in addition provides message recovery is provided.
Abstract: We describe an RSA-based signing scheme which combines essentially optimal efficiency with attractive security properties. Signing takes one RSA decryption plus some hashing, verification takes one RSA encryption plus some hashing, and the size of the signature is the size of the modulus. Assuming the underlying hash functions are ideal, our schemes are not only provably secure, but are so in a tight way-- an ability to forge signatures with a certain amount of computational resources implies the ability to invert RSA (on the same size modulus) with about the same computational effort. Furthermore, we provide a second scheme which maintains all of the above features and in addition provides message recovery. These ideas extend to provide schemes for Rabin signatures with analogous properties; in particular their security can be tightly related to the hardness of factoring.
1,079 citations
TL;DR: All patients with articulatory planning deficits had lesions that included a discrete region of the left precentral gyms of the insula, a cortical area beneath the frontal and temporal lobes that seems to be specialized for the motor planning of speech.
Abstract: HUMAN speech requires complex planning and coordination of mouth and tongue movements. Certain types of brain injury can lead to a condition known as apraxia of speech, in which patients are impaired in their ability to coordinate speech movements but their ability to perceive speech sounds, including their own errors, is unaffected1,3. The brain regions involved in coordinating speech, however, remain largely unknown. In this study, brain lesions of 25 stroke patients with a disorder in the motor planning of articulatory movements were compared with lesions of 19 patients without such deficits. A robust double dissociation was found between these two groups. All patients with articulatory planning deficits had lesions that included a discrete region of the left precentral gyms of the insula, a cortical area beneath the frontal and temporal lobes. This area was completely spared in all patients without these articulation deficits. Thus this area seems to be specialized for the motor planning of speech.
1,070 citations
TL;DR: In this article, the shape and size distribution and crystallinity of the Fe3O4 nanoparticles were assessed by transmission electron microscopy and selected area electron diffraction, and very uniform and stable colloidal suspensions of the particles were synthesized.
Abstract: Synthesis of suspensions of nanosize particles of Fe3O4 was carried out in bulk aqueous solutions without the presence of surfactants. The Fe3O4 nanoparticles were oxidized to γ-Fe2O3 by direct aeration of the suspension at 100 °C. The shape and size distribution and crystallinity of the Fe3O4 nanoparticles were assessed by transmission electron microscopy and selected area electron diffraction. Very uniform and stable colloidal suspensions of the Fe3O4 nanoparticles in water could be synthesized. Oxidation of the colloidal system leads to γ-Fe2O3 nanoparticles of much larger size than Fe3O4.
TL;DR: It is shown that the thermal motions of the polymerizing filaments can produce a directed force, and this "elastic Brownian ratchet" can explain quantitatively the propulsion of Listeria and the protrusive mechanics of lamellipodia.
TL;DR: Chattering cells located in the superficial layers of the cortex intrinsically generate 20- to 70-hertz repetitive burst firing in response to suprathreshold depolarizing current injection, and exhibit pronounced oscillations in membrane potential during visual stimulation that are largely absent during periods of spontaneous activity.
Abstract: In response to visual stimulation, a subset of neurons in the striate and prestriate cortex displays synchronous rhythmic firing in the gamma frequency band (20 to 70 hertz) This finding has raised two fundamental questions: What is the functional significance of synchronous gamma-band activity and how is it generated? This report addresses the second of these two questions By means of intracellular recording and staining of single cells in the cat striate cortex in vivo, a biophysically distinct class of pyramidal neuron termed “chattering cells” is described These neurons are located in the superficial layers of the cortex, intrinsically generate 20- to 70-hertz repetitive burst firing in response to suprathreshold depolarizing current injection, and exhibit pronounced oscillations in membrane potential during visual stimulation that are largely absent during periods of spontaneous activity These properties suggest that chattering cells may make a substantial intracortical contribution to the generation of synchronous cortical oscillations and thus participate in the recruitment of large populations of cells into synchronously firing assemblies
TL;DR: In a two-wave national telephone survey, a probability sample of English-speaking adults indicated their attitudes toward gay men at Wave 1 (1990-91; n = 538) and toward both gay men and lesbians approximately 1 year later (n = 382 at Wave 2).
Abstract: In a two-wave national telephone survey, a probability sample of English-speaking adults indicated their attitudes toward gay men at Wave 1 (1990-91; n = 538) and toward both gay men and lesbians approximately 1 year later (n = 382 at Wave 2). At Wave 1, heterosexuals reporting interpersonal contact (31.3%) manifested more positive attitudes toward gay men than those without contact. Their attitudes were more favorable to the extent that they reported more relationships, closer relationships, and receiving direct disclosure about another's homosexuality. At Wave 2, these findings were generally replicated for attitudes toward lesbians as well as gay men. Cross-wave analyses suggest a reciprocal relationship between contact and attitudes. Theoretical and policy implications of the results are discussed, with special attention to the role of interpersonal disclosure in reducing stigma based on a concealable status.
TL;DR: In this paper, the role of the medial temporal lobe in novelty processing was examined in patients with damage to the posterior hippocampal region, and it was shown that unexpected novel stimuli produce a characteristic ERP signal, accompanied by an autonomic skin response.
Abstract: THE ability to respond to unexpected stimuli (the 'orienting response') is a fundamental characteristic of mammalian behaviour1, but the brain mechanisms by which novelty is detected remain poorly defined. Electrophysiological recordings of scalp and intracranial event-related potentials (ERPs) have shown that novel stimuli activate a distributed network involving prefrontal and posterior association cortex2–6. In addition, ERP7,8 and single-neuron9,10 recordings, as well as neuroimaging11 and modelling12 studies, have suggested that temporal cortical regions, including the hippocampus, are also involved. To examine further the role of the medial temporal lobe in novelty processing, I measured physiological responses to novel auditory and tactile stimuli in patients with damage to the posterior hippocampal region. In normal control subjects, unexpected novel stimuli produce a characteristic ERP signal, accompanied by an autonomic skin response. Both responses are reduced in hippocampal lesion patients, whereas the response to expected control stimuli is unaffected. Thus the hippocampal region, in addition to its known role in memory formation, is an essential component of the distributed limbic–cortical network that detects and responds to novel stimuli.
TL;DR: The present results substantiate the idea that severity of memory impairment is dependent on locus and extent of damage within the hippocampal formation and that damage to the hippocampusal formation can cause temporally graded retrograde amnesia.
Abstract: Patient RB (Human amnesia and the medial temporal region: enduring memory impairment following a bilaterial lesion limited to field CA1 of the hippocampus, S. Zola-Morgan, L. R. Squire, and D. G. Amaral, 1986, J Neurosci 6:2950–2967) was the first reported case of human amnesia in which detailed neuropsychological analyses and detailed postmortem neuropathological analyses demonstrated that damage limited to the hippocampal formation was sufficient to produce anterograde memory impairment. Neuropsychological and postmortem neuropathological findings are described here for three additional amnesic patients with bilateral damage limited to the hippocampal formation. Findings from these patients, taken together with the findings from patient RB and other amnesic patients, make three important points about memory. (1) Bilateral damage limited primarily to the CA1 region of the hippocampal formation is sufficient to produce moderately severe anterograde memory impairment. (2) Bilateral damage beyond the CA1 region, but still limited to the hippocampal formation, can produce more severe anterograde memory impairment. (3) Extensive, temporally graded retrograde amnesia covering 15 years or more can occur after damage limited to the hippocampal formation. Findings from studies with experimental animals are consistent with the findings from amnesic patients. The present results substantiate the idea that severity of memory impairment is dependent on locus and extent of damage within the hippocampal formation and that damage to the hippocampal formation can cause temporally graded retrograde amnesia.
TL;DR: This work presents a conceptual model of aquatic invasions and a dozen empirically-derived rules that seem to govern most aquaticinvasions, and finds that these rules do seem to have more predictive value than rules derived from community assembly theory.
TL;DR: The inadequacy of dispersal data obtained directly by traditional methods using population studies of marked individuals is highlighted by comparing the resulting distributions with dispersal estimates obtained by radio-tracking and by using genetic estimates of gene flow.
Abstract: Dispersal is of central importance to population biology, behavioral ecology and conservation. However, because field studies are based on finite study areas, nearly all dispersal distributions for vertebrates currently available are biased, often highly so. The inadequacy of dispersal data obtained directly by traditional methods using population studies of marked individuals is highlighted by comparing the resulting distributions with dispersal estimates obtained by radio-tracking and by using genetic estimates of gene flow.
TL;DR: The technical aspects of gating the radiotherapy beam synchronously with respiration are dealt with: the optimal respiration monitoring system, measurements of organ displacement and linear accelerator gating.
Abstract: In order to optimize external-beam conformal radiotherapy, patient movement during treatment must be minimized. For treatment on the upper torso, the target organs are known to move substantially due to patient respiration. This paper deals with the technical aspects of gating the radiotherapy beam synchronously with respiration: the optimal respiration monitoring system, measurements of organ displacement and linear accelerator gating. Several respiration sensors including a thermistor, a thermocouple, a strain gauge and a pneumotachograph were examined to find the optimal sensor. The magnitude of breast, chest wall and lung motion were determined using playback of fluoroscopic x-ray images recorded on a VCR during routine radiotherapy simulation. Total dose, beam symmetry and beam uniformity were examined to determine any effects on the Varian 2100C linear accelerator due to gating.
TL;DR: In this paper, the biophysical, biochemical, and optical properties of 63 fresh leaves and 58 dry leaves were measured to investigate the potential of remote sensing to estimate the leaf biochemistry from space.
TL;DR: In this article, the volume averaged momentum equation is used to derive Darcy's law with the Forchheimer correction for homogeneous porous media, and the closure problem can be used to prove that F is a linear function of the velocity, and order of magnitude analysis suggests that this linear dependence may persist for a wide range of Reynolds numbers.
Abstract: In this paper we illustrate how the method of volume averaging can be used to derive Darcy's law with the Forchheimer correction for homogeneous porous media. Beginning with the Navier-Stokes equations, we find the volume averaged momentum equation to be given by
$$\langle v_\beta \rangle = - \frac{K}{{\mu _\beta }} \cdot (
abla \langle p_\beta \rangle ^\beta - \rho _\beta g) - F\cdot \langle v_\beta \rangle .$$
The Darcy's law permeability tensor, K, and the Forchheimer correction tensor, F, are determined by closure problems that must be solved using a spatially periodic model of a porous medium. When the Reynolds number is small compared to one, the closure problem can be used to prove that F is a linear function of the velocity, and order of magnitude analysis suggests that this linear dependence may persist for a wide range of Reynolds numbers.
TL;DR: A state diagram for trehalose glass is presented and it is suggested that the efficacy of this sugar for stabilization may be related to its higher glass transition temperatures at all water contents, which are higher than ambient temperatures.
TL;DR: It is concluded that the fundamental elements of apoptosis, as characterized in animals, are conserved in plants and may be used to characterize further signaling pathways leading to apoptosis in plants.
Abstract: The host-selective AAL toxins secreted by Alternaria alternata f sp lycopersici are primary chemical determinants in the Alternaria stem canker disease of tomato. The AAL toxins are members of a new class of sphinganine analog mycotoxins that cause cell death in both animals and plants. Here, we report detection of stereotypic hallmarks of apoptosis during cell death induced by these toxins in tomato. DNA ladders were observed during cell death in toxin-treated tomato protoplasts and leaflets. The intensity of the DNA ladders was enhanced by Ca2+ and inhibited by Zn2+. The progressive delineation of fragmented DNA into distinct bodies, coincident with the appearance of DNA ladders, also was observed during death of toxin-treated tomato protoplasts. In situ analysis of cells dying during development in both onion root caps and tomato leaf tracheary elements revealed DNA fragmentation localized to the dying cells as well as the additional formation of apoptotic-like bodies in sloughing root cap cells. We conclude that the fundamental elements of apoptosis, as characterized in animals, are conserved in plants. The apoptotic process may be expressed during some developmental transitions and is the functional process by which symptomatic lesions are formed in the Alternaria stem canker disease of tomato. Sphinganine analog mycotoxins may be used to characterize further signaling pathways leading to apoptosis in plants.
TL;DR: In order to develop a diagnostic tool to identify phytoplasmas and classify them according to their phylogenetic group, the sequence diversity of the 16S-23S intergenic spacer regions (SRs) of phy toplasmas was taken advantage.
Abstract: In order to develop a diagnostic tool to identify phytoplasmas and classify them according to their phylogenetic group, we took advantage of the sequence diversity of the 16S-23S intergenic spacer regions (SRs) of phytoplasmas. Ten PCR primers were developed from the SR sequences and were shown to amplify in a group-specific fashion. For some groups of phytoplasmas, such as elm yellows, ash yellows, and pear decline, the SR primer was paired with a specific primer from within the 16S rRNA gene. Each of these primer pairs was specific for a specific phytoplasma group, and they did not produce PCR products of the correct size from any other phytoplasma group. One primer was designed to anneal within the conserved tRNA(Ile) and, when paired with a universal primer, amplified all phytoplasmas tested. None of the primers produced PCR amplification products of the correct size from healthy plant DNA. These primers can serve as effective tools for identifying particular phytoplasmas in field samples.
TL;DR: In this paper, the authors evaluated the antioxidant activity of a commercial rosemary extract and the active constituents carnosol, carnosic acid, and rosmarinic acid in inhibiting the formation and decomposition of hydroperoxides in tocopherol-stripped corn oil and in corresponding corn oil-in-water emulsions.
Abstract: This study was aimed at evaluating the antioxidant activity of a commercial rosemary extract and the active constituents carnosol, carnosic acid, and rosmarinic acid, in inhibiting the formation and decomposition of hydroperoxides in tocopherol-stripped corn oil and in the corresponding corn oil-in-water emulsions. In bulk corn oil, the rosemary extract, carnosic acid, rosmarinic acid, and α-tocopherol were significantly more active than carnosol. In contrast, in corn oil-in-water emulsion, the rosemary compounds were less active than in bulk oil, and the rosemary extract, carnosic acid, carnosol, and α-tocopherol were more active than rosmarinic acid. Similar results were obtained in corn oil-in-water phosphate buffer emulsion at pH 5, but α-tocopherol was less active. Carnosol and carnosic acid were much more active antioxidants in corn oil-in-water emulsions buffered at pH 4 and 5 than at pH 7. The decreased antioxidant activity of the polar hydrophilic rosemary compounds in the emulsion system may be ...
TL;DR: Data demonstrate that the cat flea readily transmits B. henselae to cats, and control of feline infestation with this arthropod vector may provide an important strategy for the prevention of infection of both humans and cats.
Abstract: Bartonella henselae is an emerging bacterial pathogen, causing cat scratch disease and bacillary angiomatosis. Cats bacteremic with B. henselae constitute a large reservoir from which humans become infected. Prevention of human infection depends on elucidation of the natural history and means of feline infection. We studied 47 cattery cats in a private home for 12 months to determine the longitudinal prevalence of B. henselae bacteremia, the prevalence of B. henselae in the fleas infesting these cats, and whether B. henselae is transmitted experimentally to cats via fleas. Vector-mediated transmission of B.henselae isolates was evaluated by removing fleas from the naturally bacteremic, flea-infested cattery cats and transferring these fleas to specific-pathogen-free (SPF) kittens housed in a controlled, arthropod-free University Animal Facility. B. henselae bacteremia was detected in 89% of the 47 naturally infected cattery cats. A total of 132 fleas were removed from cats whose blood was simultaneously cultured during different seasons and were tested individually for the presence of B. henselae DNA by PCR. B. henselae DNA was detected in 34% of 132 fleas, with seasonal variation, but without an association between the presence or the level of bacteremia in the corresponding cat. Cat fleas removed from bacteremic cattery cats transmitted B. henselae to five SPF kittens in two separate experiments; however, control SPF kittens housed with highly bacteremic kittens in the absence of fleas did not become infected. These data demonstrate that the cat flea readily transmits B. henselae to cats. Control of feline infestation with this arthropod vector may provide an important strategy for the prevention of infection of both humans and cats.
TL;DR: A multicommodity flow formulation combined with randomized rounding is employed to calculate the routes for lightpaths in large optical networks in which nodes employ wavelength-routing switches which enable the establishment of wavelength-division-multiplexed channels between node pairs.
Abstract: We consider large optical networks in which nodes employ wavelength-routing switches which enable the establishment of wavelength-division-multiplexed (WDM) channels, called lightpaths, between node pairs. We propose a practical approach to solve routing and wavelength assignment (RWA) of lightpaths in such networks. A large RWA problem is partitioned into several smaller subproblems, each of which may be solved independently and efficiently using well-known approximation techniques. A multicommodity flow formulation combined with randomized rounding is employed to calculate the routes for lightpaths. Wavelength assignments for lightpaths are performed based on graph-coloring techniques. Representative numerical examples indicate the accuracy of our algorithms.
TL;DR: The data suggest that during infection the pathogen delivers AvrPto into the plant host cell and that resistance is specified by direct interaction of Pto with AvRPto.
Abstract: Transient expression of the Pseudomonas syringae avirulence gene avrPto in plant cells resulted in a Pto-dependent necrosis. The AvrPto avirulence protein was observed to interact directly with the Pto resistance protein in the yeast two-hybrid system. Mutations in the Pto and avrPto genes which reduce in vivo activity had parallel effects on association in the two-hybrid assay. These data suggest that during infection the pathogen delivers AvrPto into the plant host cell and that resistance is specified by direct interaction of Pto with AvrPto.
TL;DR: In this paper, wine phenolic fractions of a Petite Syrah wine were evaluated for their antioxidant activity in inhibiting LDL oxidation in vitro, and the most active fractions contained components of the catechin family.
Abstract: Current research suggests that wine contains substances that may reduce the mortality rate from coronary diseases. The oxidation of low-density lipoprotein (LDL) is thought to be a key step in the development of atherosclerosis. Phenolic fractions of a Petite Syrah wine were evaluated for their antioxidant activity in inhibiting LDL oxidation in vitro. The more active fractions contained components of the catechin family. The catechin oligomers and the procyanidin dimers (B 2 , B 3 , B 4 , B 6 , B 8 ) and trimers (C 1 , C 2 ) were extracted, isolated and purified from grapes seeds. These compounds were tested for their inhibition of LDL oxidation, along with other monomeric wine phenolics. The procyanidin dimers B 2 and B 8 , and trimer C 1 , and the monomers catechin, epicatechin and myricetin had the highest antioxidant activity. The procyanidin dimers B 3 , B 4 and C 2 and the monomers gallic acid, quercetin, caffeic acid, and rutin, and a group of compounds that included the dimer B 6 , ellagic acid, sinapic acid, cyanidin had lower antioxidant activity and α-tocopherol had the least activity. Thus, the numerous phenolic compounds found in wine are potent antioxidants in inhibiting LDL oxidation in vitro.