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2005

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Articles 4441 - 4470 of 5573

Full-Text Articles in Physical Sciences and Mathematics

Quasi-Static Analysis Of Defected Ground Structure, Nemai C. Karmakar, Sushim Mukul Roy, Isaac Balbin, Gerhard F. Swiegers Jan 2005

Quasi-Static Analysis Of Defected Ground Structure, Nemai C. Karmakar, Sushim Mukul Roy, Isaac Balbin, Gerhard F. Swiegers

Faculty of Science - Papers (Archive)

A quasi-static equivalent circuit model of a dumbbell shaped defected ground structure (DGS) is developed. The equivalent circuit model is derived from the equivalent inductance and capacitance developed due to the perturbed returned current path on the ground and the narrow gap, respectively. The theory is validated against the commercial full-wave solver CST Microwave Studio. Finally, the calculated results are compared with the measured results. Good agreement between the theory, the commercially available numerical analyses and the experimental results validates the developed theoretical model.

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Evidence For Altitude-Dependent Photolysis-Induced 18o Isotopic Fractionation In Stratospheric Ozone, Vanessa E. Haverd, Geoffrey C. Toon, David W. Griffith Jan 2005

Evidence For Altitude-Dependent Photolysis-Induced 18o Isotopic Fractionation In Stratospheric Ozone, Vanessa E. Haverd, Geoffrey C. Toon, David W. Griffith

Faculty of Science - Papers (Archive)

We present vertical profiles of 18O fractionations in ozone, measured by balloon-borne infrared remote sensing between 15 and 40 km. The magnitudes of the 16O16O18O (668O3) and 16O18O16O (686O3) fractionations are 13.5 +/- 2.7% and 7.7 +/- 2.2%, averaged over the 20-35 km altitude range, in good agreement with previous atmospheric measurements by mass spectrometry and both infrared and far infrared remote sensing spectroscopy. We use our fractionation profiles, together with known fractionation effects of the ozone formation reaction, to deduce …

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Tropical Cyclone Disturbance Of Coral Communities Of The Great Barrier Reef, 1969-2003, Marjetta L. Puotinen Jan 2005

Tropical Cyclone Disturbance Of Coral Communities Of The Great Barrier Reef, 1969-2003, Marjetta L. Puotinen

Faculty of Science - Papers (Archive)

The primary building block of coral reef ecosystems, whether an isolated mid-ocean atoll or a complex system of thousands of reefs, are the individual coral colonies that combine to form the reef structures which host coral communities. The state of a coral reef community (i.e. percentage coral coverage, dominant growth forms and size classes), or any other ecosystem, at any given time is the result of interactions between a range of disturbances and routine ecological processes that operate across a continuum of spatial and temporal scales (Gunderson et al 2002). The biological (living coral colonies) and structural (dead coral framework …

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Factors Affecting Metal Releases From Contaminated Marine Sediments, Dianne F. Jolley, Clare A. Atkinson, Stuart L. Simpson Jan 2005

Factors Affecting Metal Releases From Contaminated Marine Sediments, Dianne F. Jolley, Clare A. Atkinson, Stuart L. Simpson

Faculty of Science - Papers (Archive)

In aquatic environments, the depth of oxygen penetration into sediment depends on sediment texture, porosity, permeability and the extent of biological (e.g., bioturbation) and physical (e.g., wave action) processes. Below the oxygen penetration depth (generally 10 mm) anoxic conditions prevail and bacteria use other oxidants such as iron and manganese oxides and sulfate to breakdown organic matter. The bacteria-catalysed reduction of sulfate releases hydrogen sulfide according to Equation 1. The release of H2S into the pore waters SO42- + bacteria → H2S (Equation 1).

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Aboriginal Pastoralism, Social Embeddedness And Cultural Continuity In Central Australia, Nicholas J. Gill Jan 2005

Aboriginal Pastoralism, Social Embeddedness And Cultural Continuity In Central Australia, Nicholas J. Gill

Faculty of Science - Papers (Archive)

Aboriginal people are involved in pastoral enterprises throughout the inland and north of Australia. This has generated difficulties as landowners and policymakers struggled with conflicts between Aboriginal social structures and the demands of running commercial businesses. Problems often arose due to imposition of nonindigenous norms regarding land use. It has been suggested that pastoralism can generate social and cultural benefits for Aboriginal landowners, but these have not been investigated in any detail. Drawing on the concept of social embeddedness and fieldwork with Aboriginal pastoralists, this article identifies, describes, and ranks sociocultural benefits arising from Aboriginal pastoralism. Pastoralism fulfilled uniquely Aboriginal …

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The Genomic Island Sgii, Containing The Multiple Antibiotic Resistance Region Of Salmonella Enterica Serovar Typhimurium Dt104 Or Variants Of It, Is Widely Distributed In Other S-Enterica Serovars, Renee Levings, Diane Lightfoot, Sally R. Partridge, Ruth M. Hall, Steven P. Djordjevic Jan 2005

The Genomic Island Sgii, Containing The Multiple Antibiotic Resistance Region Of Salmonella Enterica Serovar Typhimurium Dt104 Or Variants Of It, Is Widely Distributed In Other S-Enterica Serovars, Renee Levings, Diane Lightfoot, Sally R. Partridge, Ruth M. Hall, Steven P. Djordjevic

Faculty of Science - Papers (Archive)

The global dissemination of the multiply-antibiotic-resistant Salmonella entericaserovar Typhimurium DT104 clone with the resistance genes located in a class 1 integron, here designated In104, within genomic island SGI1 is a significant public health issue. Here, we have shown that SGI1 and variants of it carrying different combinations of resistance genes are found in several Salmonella enterica serovars. These are serovars Cerro, Derby, Dusseldorf, Infantis, Kiambu, and Paratyphi B dT+ isolated from human infections and serovar Emek from sewage effluent. Two new variants, SGI1-I and SGI1-J, both of which include thedfrA1-orfC cassette array, were identified.

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Latitude And Altitude Variability Of Carbon Monoxide In The Atlantic Detected From Ship-Borne Fourier Transform Spectrometry, Model, And Satellite Data, Voltaire A. Velazco, Justus Notholt, Thorsten Warneke, Mark Lawrence, Holger Bremer, James Drummond, Astrid Schulz, Jurgen Krieg, O. Schrems Jan 2005

Latitude And Altitude Variability Of Carbon Monoxide In The Atlantic Detected From Ship-Borne Fourier Transform Spectrometry, Model, And Satellite Data, Voltaire A. Velazco, Justus Notholt, Thorsten Warneke, Mark Lawrence, Holger Bremer, James Drummond, Astrid Schulz, Jurgen Krieg, O. Schrems

Faculty of Science - Papers (Archive)

Carbon monoxide (CO) volume mixing ratio (VMR) profiles have been retrieved from ship-borne solar absorption spectra recorded in the Atlantic between 80°N and 70°S. CO profiles can be retrieved up to 30 km with a maximum altitude resolution of 4 km for a few layers. CO enhancements due to biomass burning have been detected. Recurring enhancements of CO were detected in the upper troposphere (10–15 km) in the equatorial regions and in the southern Atlantic (20°S–30°S). These enhancements could be traced back to African biomass burning sources as well as sources as far as South America. Similar results are observed …

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A Methodology For Identifying And Formalizing Farmers’ Representations Of Watershed Management: A Case Study From Northern Thailand, N Becu, O Barreteau, Pascal Perez, J Saising, S Sungted Jan 2005

A Methodology For Identifying And Formalizing Farmers’ Representations Of Watershed Management: A Case Study From Northern Thailand, N Becu, O Barreteau, Pascal Perez, J Saising, S Sungted

SMART Infrastructure Facility - Papers

Linking modeling tools and the participatory approach for development is not a common combination. Participatory multi-agent system modeling (PMASM) is a tool for sharing viewpoints among stakeholders and facilitating the negotiation process. A key question of this approach is the acquisition and the modeling of the various stakeholders’ representations. Our research team, whose Asian branch is represented in this book, tries to formalize the passage from fieldwork to the model by defining a methodology that can be implemented in the field. This methodology adapts knowledge engineering acquisition techniques to in-field stakeholders’ representations for PMASM. In a northern Thailand watershed, we …

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Planning For Natural Hazards — How Can We Mitigate The Impacts?, Edward A. Bryant, Lesley M. Head, J. Morrison Jan 2005

Planning For Natural Hazards — How Can We Mitigate The Impacts?, Edward A. Bryant, Lesley M. Head, J. Morrison

Faculty of Science - Papers (Archive)

Australia has the same frequency of natural hazards as any other continent; however, the types and impact of hazards are very different. Globally, the deadliest hazards are floods, earthquakes, tropical storms and tsunami. In Australia, the deadliest hazards are heat waves, floods, tropical cyclones and bushfires. Similarly, while the most expensive hazards ranked globally are also floods, earthquakes and tropical cyclones, in Australia, the costliest hazards are tropical storms, floods, wind and bushfires. Our isolated population distribution, together with rugged topography along the eastern and southern coastal fringe where the bulk of the population is concentrated, has lead to a …

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Surface Analyses And Immune Reactivities Of Major Cell Wall-Associated Proteins Of Group A Streptococcus, J. N. Cole, R. D. Ramirez, B. J. Currie, S. J. Cordwell, S. P. Djordjevic, Mark J. Walker Jan 2005

Surface Analyses And Immune Reactivities Of Major Cell Wall-Associated Proteins Of Group A Streptococcus, J. N. Cole, R. D. Ramirez, B. J. Currie, S. J. Cordwell, S. P. Djordjevic, Mark J. Walker

Faculty of Science - Papers (Archive)

A proteomic analysis was undertaken to identify cell-wall associated proteins of Streptococcus pyogenes. Seventy-four distinct cell-wall associated proteins were identified, 66 of which were novel. Thirty-three proteins were immunoreactive with pooled S. pyogenes-reactive human antisera. Biotinylation of the GAS cell-surface identified 23 cellwall associated proteins that are surface exposed.

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A New Strategy To Improve Proactive Route Updates In Mobile Ad Hoc Networks, Mehran Abolhasan, Tadeusz A. Wysocki, Justin Lipman Jan 2005

A New Strategy To Improve Proactive Route Updates In Mobile Ad Hoc Networks, Mehran Abolhasan, Tadeusz A. Wysocki, Justin Lipman

Faculty of Informatics - Papers (Archive)

This paper presents two new route update strategies for performing proactive route discovery in mobile ad hoc networks (MANETs). The first strategy is referred to as minimum displacement update routing (MDUR). In this strategy, the rate at which route updates are sent into the network is controlled by how often a node changes its location by a required distance. The second strategy is called minimum topology change update (MTCU). In this strategy, the route updating rate is proportional to the level of topology change each node experiences. We implemented MDUR and MTCU on top of the fisheye state routing (FSR) …

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Identity-Based Partial Message Recovery Signatures (Or How To Shorten Id-Based Signatures), Fangguo Zhang, Willy Susilo, Yi Mu Jan 2005

Identity-Based Partial Message Recovery Signatures (Or How To Shorten Id-Based Signatures), Fangguo Zhang, Willy Susilo, Yi Mu

Faculty of Informatics - Papers (Archive)

We propose a new notion of short identity-based signature scheme. We argue that the identity-based environment is essential in some scenarios. The notion of short identity-based signature schemes can be viewed as identity-based (partial) message recovery signatures. Signature schemes with message recovery has been extensively studied in the literature. This problem is somewhat related to the problem of signing short messages using a scheme that minimizes the total length of the original message and the appended signature. In this paper, firstly, we revisit this notion and propose an identity-based message recovery signature scheme. Our scheme can be regarded as the …

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Revised Land Freight External Costs In Australia, Philip Laird Jan 2005

Revised Land Freight External Costs In Australia, Philip Laird

Faculty of Informatics - Papers (Archive)

Publications in Australia to 1999 that comment on transport externalities include the former Inter-State Commission (ISC - 1990), the National Transport Planning Taskforce (NTPT - 1994) Victorian Environment Protection Authority (1994), Simpson and London (1995), Manins (1997), Brindle et al (1999), and the Bureau of Transport Economics (BTE - 1999). As noted by the ISC (1990, p89), road external costs are "…costs imposed outside market transactions and they fall on a number of individuals or groups - road users other than those individuals who give rise to the costs, individuals other than road users (such as those who live in …

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Factors Associated With Trends In Bare Ground In High Country, Heather North, Kenneth G. Russell Jan 2005

Factors Associated With Trends In Bare Ground In High Country, Heather North, Kenneth G. Russell

Faculty of Informatics - Papers (Archive)

Soil erosion in the Canterbury high country has been a concern for many years, and Environment Canterbury wishes to encourage land management practices that will preserve soil quality and vegetative cover. Environment Canterbury brought to MISG2005 a data set spanning three decades of bare ground monitoring in the Canterbury high country, along with data on factors with potential to impact on the processes of revegetation. These include topographic and climate data, soil nutrient status and land management factors. The study group analysed these data with the aim of determining whether trends in bare ground can be predicted from the potential …

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Exploring End-User Perceptions Towards Mandated Deployment Of Pda-Based Health Information Systems Within Ambulatory Care, Jason P. Sargent, Lois Burgess, Joan Cooper, Carole Alcock, Damien Ryan Jan 2005

Exploring End-User Perceptions Towards Mandated Deployment Of Pda-Based Health Information Systems Within Ambulatory Care, Jason P. Sargent, Lois Burgess, Joan Cooper, Carole Alcock, Damien Ryan

Faculty of Informatics - Papers (Archive)

The impact of many well intentioned technology integration projects has not always been viewed favourably. In fact, many projects are destined to fail from the outset by not considering fundamental IT system inves tment risks (technical failure, data failure, user failure, organizational failure) [Lyytinen & Hirschiem, 1987]. With any new technology ‘an element of uncertainty exists in the minds of decision makers with respect to the successful adoption of them’ [Bagozzi et al, 1992]. Uncertainty towards adopting new technologies is not solely the domain of decision makers. Apart from chief technology and information officers, system administrators and help desk personnel, …

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The Character Of Free Topological Groups Ii, Peter Nickolas, Mikhail Tkachenko Jan 2005

The Character Of Free Topological Groups Ii, Peter Nickolas, Mikhail Tkachenko

Faculty of Informatics - Papers (Archive)

A systematic analysis is made of the character of the free and free abelian topological groups on metrizable spaces and compact spaces, and on certain other closely related spaces. In the first case, it is shown that the characters of the free and the free abelian topological groups on X are both equal to the “small cardinal” d if X is compact and metrizable, but also, more generally, if X is a non-discrete k!-space all of whose compact subsets are metrizable, or if X is a non-discrete Polish space. An example is given of a zero-dimensional separable metric space for …

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Critical Questions In Computational Models Of Legal Argument, Douglas Walton, Thomas F. Gordon Jan 2005

Critical Questions In Computational Models Of Legal Argument, Douglas Walton, Thomas F. Gordon

CRRAR Publications

Two recent computational models of legal argumentation, by Verheij and Gordon respectively, have interpreted critical questions as premises of arguments that can be defeated using Pollock’s concepts of undercutters and rebuttals. Using the scheme for arguments from expert opinion as an example, this paper evaluates and compares these two models of critical questions from the perspective of argumentation theory and competing legal theories about proof standardsfor defeating presumptions. The applicable proof standard is found to be a legal issue subject to argument. Verheij’smodel is shown to have problems because the proof stan-dards it applies to different kinds of premises are …

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The Moths Of Neal Smith National Wildlife Refuge: A Preliminary Assessment, Michelle N. Lewis, Renae M. Steichen, Keith S. Summerville Jan 2005

The Moths Of Neal Smith National Wildlife Refuge: A Preliminary Assessment, Michelle N. Lewis, Renae M. Steichen, Keith S. Summerville

Journal of the Iowa Academy of Science: JIAS

North American prairie systems are believed to have supported substantial insect biodiversity. Loss of prairie and oak savanna habitats, however, has been severe in many Midwestern states, including Iowa. An unanswered question facing land managers interested in restoring tallgrass prairies to the Iowan landscape is the degree to which restored habitats contain native insect species that are dependent upon prairie habitat. This study reports data from a preliminary survey of the moths of Neal Smith National Wildlife Refuge, a 2,292-ha prairie and oak savanna restoration site in central Iowa. We identified and cataloged a total of 426 species of moths …

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Cover - Table Of Contents Jan 2005

Cover - Table Of Contents

Journal of the Iowa Academy of Science: JIAS

No abstract provided.

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Letter To The Editor - Conservation Of Freshwater Mussels In Iowa, K. Elizabeth Poole Jan 2005

Letter To The Editor - Conservation Of Freshwater Mussels In Iowa, K. Elizabeth Poole

Journal of the Iowa Academy of Science: JIAS

Freshwater mussels occur in a variety of aquatic ecosystems worldwide but nowhere is mussel species richness as high as is reported in North America. With nearly 300 recorded species in the U.S., mussels are key components of freshwater biodiversity playing a vital role in benthic communities. Ecologically important in biological processing and nutrient cycling, mussels are also an important food item for a variety of mammals including mink, otter, and raccoon. In addition to ecological importance, freshwater mussels have been economically important in the production of cultured pearls.

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Discordant Harmonies In Fingernail Clam Populations (Musculium Transversum) Of Mississippi River Backwater Lakes, Jim Eckblad Jan 2005

Discordant Harmonies In Fingernail Clam Populations (Musculium Transversum) Of Mississippi River Backwater Lakes, Jim Eckblad

Journal of the Iowa Academy of Science: JIAS

The populations of Musculium transversum from 8 backwater lakes have been studied over a 29-year period based upon over 440 grab samples. These lakes in Navigation Pool 9 of the Upper Mississippi River (UMR) range in size from 2 to 255 hectare surface area, mean depths from 0.2 to 0.9 meters, with mean water exchange times from 0.5 to almost 57 hours. Samples from the 1989-91 period suggested summer Muscu!ium populations had declined to about 9 percent of their mid-1970 levels. Deterministic models have attempted to explain this decline. More recent sampling suggests a substantial recovery of Musculium populations (mid-summer …

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Index For The Journal Of The Iowa Academy Of Science Volume 112 Jan 2005

Index For The Journal Of The Iowa Academy Of Science Volume 112

Journal of the Iowa Academy of Science: JIAS

No abstract provided.

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Cover - Table Of Contents Jan 2005

Cover - Table Of Contents

Journal of the Iowa Academy of Science: JIAS

No abstract provided.

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Iowa's Sand Prairie State Preserves: Anomalous Grain-Size Distributions And Optically Stimulated Luminescence (Osl) Dates, Steven H. Emerman, Brian R. Depew, Lisa K. Anderson Jan 2005

Iowa's Sand Prairie State Preserves: Anomalous Grain-Size Distributions And Optically Stimulated Luminescence (Osl) Dates, Steven H. Emerman, Brian R. Depew, Lisa K. Anderson

Journal of the Iowa Academy of Science: JIAS

Grain-size distributions and optically stimulated luminescence (OSL) dates were obtained for the sand from Iowa's five sand prairie state preserves, which are Behren's Ponds and Woodland, Cedar Hills Sand Prairie, Kish-Ke-Kosh Prairie, Marietta Sand Prairie and Rock Island. OSL dates ranged from the late Pleistocene (15,560 years B.P.) to the very late Holocene (as recent as 590 years B.P.), indicating that the late Pleistocene and Holocene Epochs in Iowa have seen multiple episodes of aridity, which is consistent with results from the Nebraska Sand Hills and eolian sand stringers in southeastern Minnesota. The grain-size distributions were anomalous in that, compared …

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Threatened By Industry, Saved By Science: Mussel Propagation At The Fairport Biological Laboratory, James Pritchard Jan 2005

Threatened By Industry, Saved By Science: Mussel Propagation At The Fairport Biological Laboratory, James Pritchard

Journal of the Iowa Academy of Science: JIAS

During the 1890s, people on the Mississippi River exploited mussel populations to support a thriving button industry. Within a brief time, they noticed significant declines in mussel populations, and called on the U.S. Bureau of Fisheries to save the resource. This paper discusses mussel propagation studies, techniques, and activities carried on in association with the Fairport Biological Laboratory (Iowa) from about 1908 to 1932. While scientists developed sophisticated techniques and had success in mussel propagation, changing habitat conditions in the river (caused mainly by pollution and dam construction) meant limited success in rescuing mussel stocks, while the introduction of plastic …

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Aspects Of An Interior Stream Clam Midden From 1915 At Quasqueton, Buchanan County Iowa, Dennis W. Schlicht Jan 2005

Aspects Of An Interior Stream Clam Midden From 1915 At Quasqueton, Buchanan County Iowa, Dennis W. Schlicht

Journal of the Iowa Academy of Science: JIAS

During clam surveys on the Wapsipinicon River in 1991 buried clams were observed in a bank of the river at Quasqueton, Buchanan County, Iowa. An interview with the landowner revealed that the clams were from a 1915 local clamming operation. Excavation and examination of many of the clams reveal interesting differences in species composition and size, when compared to more recent specimens from the river. Observations on the midden were recorded, species determinations were made and measurements were taken. Comparisons are made to two other modern surface surveys on the river. Differences were observed in both species composition and shell …

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The Unionid Mussels (Mollusca: Bivalvia: Unionidae) Of Missouri River Floodplain Ditches In Fremont County Southwestern Iowa And Atchison And Holt Counties Northwestern Missouri, Ellet Hoke Jan 2005

The Unionid Mussels (Mollusca: Bivalvia: Unionidae) Of Missouri River Floodplain Ditches In Fremont County Southwestern Iowa And Atchison And Holt Counties Northwestern Missouri, Ellet Hoke

Journal of the Iowa Academy of Science: JIAS

A survey of ditches in the Missouri River floodplain in southwestern Iowa and northwestern Missouri resulted in the recovery of nine unionid mollusk species. The floodplain ditches may provide valuable habitat for mussels in a region that has suffered a tremendous decrease in productive aquatic habitats over the past sixty-eight years. Additional survey activity is needed to determine the complete inventory of unionid mollusks in the area.

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Transport Of Chemical And Microbial Compounds From Known Wastewater Discharges: Potential For Use As Indicators Of Human Fecal Contamination, Susan Glassmeyer, Edward Furlong, Dana Kolpin, Jeffrey Cahill, Steven Zaugg, Stephen Werner, Michael Meyer, David Kryak Jan 2005

Transport Of Chemical And Microbial Compounds From Known Wastewater Discharges: Potential For Use As Indicators Of Human Fecal Contamination, Susan Glassmeyer, Edward Furlong, Dana Kolpin, Jeffrey Cahill, Steven Zaugg, Stephen Werner, Michael Meyer, David Kryak

United States Geological Survey: Staff Publications

The quality of drinking and recreational water is currently (2005) determined using indicator bacteria. However, the culture tests used to analyze for these bacteria require a long time to complete and do not discriminate between human and animal fecal material sources. One complementary approach is to use chemicals found in human wastewater, which would have the advantages of (1) potentially shorter analysis times than the bacterial culture tests and (2) being selected for human-source specificity. At 10 locations, water samples were collected upstream and at two successive points downstream from a waste-waster treatment plant (WWTP); a treated effluent sample was …

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Participant Observations On Environmental And Social Eff Ect S Of The Conservation Reserve Program: Results Of A National Survey, Arthur W. Alen Jan 2005

Participant Observations On Environmental And Social Eff Ect S Of The Conservation Reserve Program: Results Of A National Survey, Arthur W. Alen

United States Geological Survey: Staff Publications

A national survey of Conservation Reserve Program (CRP) contractees was completed to obtain information about environmental and social effects of the program on participants, farms, and communities. Over 75% of respondents believed CRP benefits to wildlife were important. Seventy-three percent of respondents observed increased numbers of wildlife associated with CRP lands. A majority of respondents (82%) believed the amount of assistance furnished by the U.S. Department of Agriculture related to planning and maintaining wildlife habitat associated with CRP lands was appropriate. The majority of respondents reported CRP benefits, including increased quality of surface and ground waters, improved air quality, control …

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Paleoceanographic History Of The Guaymas Basin, Gulf Of California, During The Past 15,000 Years Based On Diatoms, Silicoflagellates, And Biogenic Sediments, John A. Barron, David Bukrya, Walter E. Dean Jan 2005

Paleoceanographic History Of The Guaymas Basin, Gulf Of California, During The Past 15,000 Years Based On Diatoms, Silicoflagellates, And Biogenic Sediments, John A. Barron, David Bukrya, Walter E. Dean

United States Geological Survey: Staff Publications

High-resolution records of calcium carbonate, biogenic opal, diatoms, and silicoflagellates from western Guaymas Basin gravity core GGC55 and piston core JPC56 and eastern Guaymas Basin DSDP Site 480 reveal a complex paleoceanographic history of the central Gulf of California during the past 15,000 years. Prior to ~6.2 ka, the eastern and western Guaymas Basin proxy records were remarkably similar. After conditions similar to those of today during the Bølling–Allerod, the Younger Dryas (YD) saw a major drop in diatom production, coincident with increased calcium carbonate and tropical microfossils suggestive of El Nino-like conditions. Biosiliceous productivity began increasing during the latter …

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