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  • 1
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    Lost in transportation: Information measures and cognitive limits in multilayer navigation (2016)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2016-02-21
    Description: Cities and their transportation systems become increasingly complex and multimodal as they grow, and it is natural to wonder whether it is possible to quantitatively characterize our difficulty navigating in them and whether such navigation exceeds our cognitive limits. A transition between different search strategies for navigating in metropolitan maps has been observed for large, complex metropolitan networks. This evidence suggests the existence of a limit associated with cognitive overload and caused by a large amount of information that needs to be processed. In this light, we analyzed the world’s 15 largest metropolitan networks and estimated the information limit for determining a trip in a transportation system to be on the order of 8 bits. Similar to the "Dunbar number," which represents a limit to the size of an individual’s friendship circle, our cognitive limit suggests that maps should not consist of more than 250 connection points to be easily readable. We also show that including connections with other transportation modes dramatically increases the information needed to navigate in multilayer transportation networks. In large cities such as New York, Paris, and Tokyo, more than 80% of the trips are above the 8-bit limit. Multimodal transportation systems in large cities have thus already exceeded human cognitive limits and, consequently, the traditional view of navigation in cities has to be revised substantially.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
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    The rise of predators (2011)
    Geological Society of America (GSA)
    Details
    Publication Date: 2011-06-01
    Description: Despite their abundance, diversity, and importance today, organisms with mineralized skeletons are a relatively recent introduction. For the first three billion years of its history, life was soft-bodied, inducing mineralized structures passively, if at all. Beginning ca. 550 Ma, however, more than two dozen clades—primarily animal, but also protistan—independently evolved mineralized skeletons within a geologically short interval of time (Fig. 1; Bengtson, 1992). Now a new report by Cohen et al. (2011; p. 539 in this issue of Geology) describing beautifully intricate scale-like microfossils from the Fifteenmile Group, Yukon Territory, provides definitive evidence for mineralized skeletons some 150–250 m.y. earlier. These scale-like microfossils were first reported over two decades ago (Allison and Hilgert, 1986), but neither their age nor their mineralogy were well constrained. Work by Cohen and her colleagues has now shown that these scales (which perhaps enveloped a single-celled green alga) are between ca. 717 and ca. 812 Ma in age and composed of primary phosphate (Macdonald et al., 2010; Cohen et al., 2011). This adds to earlier suggestive evidence for mineralization at this time: the ca. 770–742 Ma vase-shaped microfossil (VSM) Melicerion poikilon, interpreted on the basis of taphonomic models to be a euglyphid amoeba whose organic-walled test was embedded with mineralized scales, possibly siliceous (Figs. 1B and 1C; Porter and Knoll, 2000; Porter et al., 2003); the mid-Neoproterozoic Tenuocharta cloudii, a multicellular, sheet-like fossil whose calcareous cell walls may reflect primary (Horodyski and Mankiewicz, 1990) or early diagenetic (Knoll, 2003) mineralization; and ca. 650 Ma millimeter- to centimeter-scale asymmetric bodies permeated with a network of canals and interpreted to be sponge-like organisms perhaps lightly mineralized with carbonate (Maloof et al., 2010b)...
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 3
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    Pervasive lower-crustal seismic anisotropy in Southern California: Evidence for underplated schists and active tectonics (2011)
    Geological Society of America (GSA)
    Details
    Publication Date: 2011-06-01
    Description: Understanding lower-crustal deformational processes and the related features that can be imaged by seismic waves is an important goal in active tectonics. We demonstrate that teleseismic receiver functions calculated for broadband seismic stations in Southern California reveal a signature of pervasive seismic anisotropy in the lower crust. The large amplitudes and small move-out of the diagnostic converted phases, as well as the broad similarity of data patterns from widely separated stations, support an origin primarily from a basal crustal layer of hexagonal anisotropy with a dipping symmetry axis. We conducted neighborhood algorithm searches for depth and thickness of the anisotropic layer and the trend and plunge of the anisotropy symmetry (slow) axis for 38 stations. The searches produced a wide range of results, but a dominant SW-NE trend of the symmetry axis emerged. When the results are divided into crustal blocks and restored to their pre–36 Ma locations, the regional-scale SW-NE trend becomes more consistent, although a small subset of the results can be attributed to NW-SE shearing related to San Andreas transform motion. We interpret this dominant trend as a fossilized fabric within schists, created from top-to-the-SW sense of shear that existed along the length of coastal California during pretransform, early Tertiary subduction or from shear that occurred during subsequent extrusion. Comparison of receiver-function common conversion point stacks to seismic models from the active Los Angeles Regional Seismic Experiment shows a strong correlation in the location of anisotropic layers with “bright” reflectors, further affirming these results.
    Print ISSN: 1941-8264
    Electronic ISSN: 1947-4253
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 4
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    Organic-walled microfossil assemblages from glacial and interglacial Neoproterozoic units of Australia and Svalbard (2014)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2014-11-04
    Description: Before the onset of the Neoproterozoic Snowball Earth glaciations, eukaryotes had begun diversifying, and in their aftermath, macroscopic life, including both animals and macroalgae, became abundant and widespread. Although glacially driven mass extinctions have been hypothesized, little is known about the biosphere during and between these glaciations. Here we present new data from organic-walled microfossil assemblages from five successions in Australia and Svalbard that collectively span the first (Sturtian) glaciation and interglacial interval and integrate them with data derived from a critical evaluation of the literature to produce a new estimate of eukaryotic diversity from 850 to 650 Ma. These new glacial and interglacial assemblages consist of only smooth-walled spheroids (leiosphaerids), aggregates of cells, and filaments, in contrast to the much more diverse organic-walled microfossil assemblages found in early Neoproterozoic rocks. This contrast is not attributed to biases in deposition or preservation, but is instead interpreted as reflecting an interval of lowered eukaryotic diversity that spanned the glaciations and that may have begun millions of years prior to their onset.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 5
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    Emerging marine diseases--climate links and anthropogenic factors (1999)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1999-09-25
    Description: Mass mortalities due to disease outbreaks have recently affected major taxa in the oceans. For closely monitored groups like corals and marine mammals, reports of the frequency of epidemics and the number of new diseases have increased recently. A dramatic global increase in the severity of coral bleaching in 1997-98 is coincident with high El Nino temperatures. Such climate-mediated, physiological stresses may compromise host resistance and increase frequency of opportunistic diseases. Where documented, new diseases typically have emerged through host or range shifts of known pathogens. Both climate and human activities may have also accelerated global transport of species, bringing together pathogens and previously unexposed host populations.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Harvell, C D -- Kim, K -- Burkholder, J M -- Colwell, R R -- Epstein, P R -- Grimes, D J -- Hofmann, E E -- Lipp, E K -- Osterhaus, A D -- Overstreet, R M -- Porter, J W -- Smith, G W -- Vasta, G R -- 1PO1 ES09563/ES/NIEHS NIH HHS/ -- New York, N.Y. -- Science. 1999 Sep 3;285(5433):1505-10.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10498537" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Aquaculture ; *Climate ; Cnidaria ; *Disease Outbreaks/*veterinary ; Humans ; Infection/epidemiology/*etiology/transmission/*veterinary ; *Marine Biology ; Oceans and Seas ; Water Pollution
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    Teratogen-mediated inhibition of target tissue response to Shh signaling (1998)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1998-06-11
    Description: Veratrum alkaloids and distal inhibitors of cholesterol biosynthesis have been studied for more than 30 years as potent teratogens capable of inducing cyclopia and other birth defects. Here, it is shown that these compounds specifically block the Sonic hedgehog (Shh) signaling pathway. These teratogens did not prevent the sterol modification of Shh during autoprocessing but rather inhibited the response of target tissues to Shh, possibly acting through the sterol sensing domain within the Patched protein regulator of Shh response.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Cooper, M K -- Porter, J A -- Young, K E -- Beachy, P A -- New York, N.Y. -- Science. 1998 Jun 5;280(5369):1603-7.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/9616123" target="_blank"〉PubMed〈/a〉
    Keywords: Abnormalities, Drug-Induced/etiology ; Animals ; Cell Membrane/metabolism ; Central Nervous System/drug effects/*embryology/metabolism ; Chick Embryo ; Cholesterol/biosynthesis/*metabolism ; Culture Techniques ; DNA-Binding Proteins/biosynthesis ; Endoplasmic Reticulum/metabolism ; Hedgehog Proteins ; Hepatocyte Nuclear Factor 3-beta ; Holoprosencephaly/chemically induced ; Homeodomain Proteins/biosynthesis ; LIM-Homeodomain Proteins ; Membrane Proteins/metabolism ; Muscle Proteins/biosynthesis ; Nerve Tissue Proteins/biosynthesis ; Nuclear Proteins/biosynthesis ; PAX7 Transcription Factor ; Proteins/*metabolism ; Receptors, Cell Surface ; Signal Transduction/drug effects ; Teratogens/*pharmacology ; Tomatine/analogs & derivatives/pharmacology ; *Trans-Activators ; *Transcription Factors ; Triparanol/pharmacology ; Veratrum Alkaloids/*pharmacology ; trans-1,4-Bis(2-chlorobenzaminomethyl)cyclohexane Dihydrochloride/pharmacology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 7
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    Evidence for substantial variations of atmospheric hydroxyl radicals in the past two decades (2001)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2001-05-05
    Description: The hydroxyl radical (OH) is the dominant oxidizing chemical in the atmosphere. It destroys most air pollutants and many gases involved in ozone depletion and the greenhouse effect. Global measurements of 1,1,1-trichloroethane (CH3CCl3, methyl chloroform) provide an accurate method for determining the global and hemispheric behavior of OH. Measurements show that CH3CCl3 levels rose steadily from 1978 to reach a maximum in 1992 and then decreased rapidly to levels in 2000 that were lower than the levels when measurements began in 1978. Analysis of these observations shows that global OH levels were growing between 1978 and 1988, but the growth rate was decreasing at a rate of 0.23 +/- 0.18% year(-2), so that OH levels began declining after 1988. Overall, the global average OH trend between 1978 and 2000 was -0.64 +/- 0.60% year(-1). These variations imply important and unexpected gaps in current understanding of the capability of the atmosphere to cleanse itself.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Prinn, R G -- Huang, J -- Weiss, R F -- Cunnold, D M -- Fraser, P J -- Simmonds, P G -- McCulloch, A -- Harth, C -- Salameh, P -- O'Doherty, S -- Wang, R H -- Porter, L -- Miller, B R -- New York, N.Y. -- Science. 2001 Jun 8;292(5523):1882-8. Epub 2001 May 3.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11337586" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 8
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    HIV-infected cells are killed by rCD4-ricin A chain (1988)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1988-11-25
    Description: The gp120 envelope glycoprotein of the human immunodeficiency virus (HIV), which is expressed on the surface of many HIV-infected cells, binds to the cell surface molecule CD4. Soluble derivatives of recombinant CD4 (rCD4) that bind gp120 with high affinity are attractive vehicles for targeting a cytotoxic reagent to HIV-infected cells. Soluble rCD4 was conjugated to the active subunit of the toxin ricin. This conjugate killed HIV-infected H9 cells but was 1/1000 as toxic to uninfected H9 cells (which do not express gp120) and was not toxic to Daudi cells (which express major histocompatibility class II antigens, the putative natural ligand for cell surface CD4). Specific killing of infected cells can be blocked by rgp120, rCD4, or a monoclonal antibody to the gp120 binding site on CD4.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Till, M A -- Ghetie, V -- Gregory, T -- Patzer, E J -- Porter, J P -- Uhr, J W -- Capon, D J -- Vitetta, E S -- CA-09082/CA/NCI NIH HHS/ -- CA-28149/CA/NCI NIH HHS/ -- CA-41081/CA/NCI NIH HHS/ -- New York, N.Y. -- Science. 1988 Nov 25;242(4882):1166-8.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Microbiology, University of Texas Southwestern Medical Center, Dallas 75235.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/2847316" target="_blank"〉PubMed〈/a〉
    Keywords: Antigens, Differentiation, T-Lymphocyte/*administration & dosage/immunology ; Binding Sites ; Cell Line ; Cell Survival ; Electrophoresis, Polyacrylamide Gel ; HIV/*immunology ; HIV Envelope Protein gp120 ; Histocompatibility Antigens Class II/immunology ; Humans ; Recombinant Proteins/administration & dosage/immunology ; Retroviridae Proteins/*immunology/metabolism ; Ricin/metabolism/*pharmacology ; T-Lymphocytes/immunology/microbiology/physiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
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    Impact assessment (1988)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1988-04-29
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Porter, A L -- New York, N.Y. -- Science. 1988 Apr 29;240(4852):587.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17840894" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 10
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    Evidence for biased gene conversion in concerted evolution of ribosomal DNA (1991)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1991-01-18
    Description: Concerted evolution is the production and maintenance of homogeneity within repeated families of DNA. Two mechanisms--unequal crossing over and biased gene conversion--have been the principal explanations of concerted evolution. Concerted evolution of ribosomal DNA (rDNA) arrays is thought to be largely the result of unequal crossing over. However, concerted evolution of rDNA in parthenogenetic lizards of hybrid origin is strongly biased toward one of two parental sequences, which is consistent with biased gene conversion as the operative mechanism. The apparent gene conversions are independent of initial genome dosage and result in homogenization of rDNA arrays across all nucleolar organizer regions.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hillis, D M -- Moritz, C -- Porter, C A -- Baker, R J -- New York, N.Y. -- Science. 1991 Jan 18;251(4991):308-10.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Zoology, University of Texas, Austin 78712.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/1987647" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Biological Evolution ; Blotting, Southern ; DNA, Ribosomal/*genetics ; Gene Conversion ; Karyotyping ; Lizards ; Nucleic Acid Hybridization ; Parthenogenesis ; Restriction Mapping
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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