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Articles 1 - 14 of 14
Full-Text Articles in Physical Sciences and Mathematics
Kernel Density Estimation Of Traffic Accidents In A Network Space, Zhixiao Xie, Jun Yan
Kernel Density Estimation Of Traffic Accidents In A Network Space, Zhixiao Xie, Jun Yan
Dr Jun Yan
A standard planar Kernel Density Estimation (KDE) aims to produce a smooth density surface of spatial point events over a 2-D geographic space. However, the planar KDE may not be suited for characterizing certain point events, such as traffic accidents, which usually occur inside a 1-D linear space, the roadway network. This paper presents a novel network KDE approach to estimating the density of such spatial point events. One key feature of the new approach is that the network space is represented with basic linear units of equal network length, termed lixel (linear pixel), and related network topology. The use …
Application Of Foreland Basin Detrital-Zircon Geochronology To The Reconstruction Of The Southern And Central Appalachian Orogen, Hyunmee Park, David Barbeau, Alan Rickenbaker, Denise Bachmann-Krug, George Gehrels
Application Of Foreland Basin Detrital-Zircon Geochronology To The Reconstruction Of The Southern And Central Appalachian Orogen, Hyunmee Park, David Barbeau, Alan Rickenbaker, Denise Bachmann-Krug, George Gehrels
David L Barbeau Jr
We report the U-Pb age distribution of detrital zircons collected from central and southern Appalachian foreland basin strata, which record changes of sediment provenance in response to the different phases of the Appalachian orogeny. Taconic clastic wedges have predominantly ca. 1080–1180 and ca. 1300–1500 Ma zircons, whereas Acadian clastic wedges contain abundant Paleozoic zircons and minor populations of 550–700 and 1900–2200 Ma zircons consistent with a Gondwanan affinity. Alleghanian clastic wedges contain large populations of ca. 980–1080 Ma and ca. 2700 Ma and older Archean zircons and fewer Paleozoic zircons than occur in the Acadian clastic wedges. The abundance of …
Slab Window Migration And Terrane Accretion Preserved By Low‐Temperature Thermochronology Of A Magmatic Arc, Northern Antarctic Peninsula, William Guenthner, David Barbeau, Peter Reiners, Stuart Thomson
Slab Window Migration And Terrane Accretion Preserved By Low‐Temperature Thermochronology Of A Magmatic Arc, Northern Antarctic Peninsula, William Guenthner, David Barbeau, Peter Reiners, Stuart Thomson
David L Barbeau Jr
Existing paleogeographic reconstructions indicate that the northern Antarctic Peninsula was central to several Mesozoic and Cenozoic tectonic events that have implications for ocean circulation and continental margin evolution. To evaluate the exhumational record of these processes, we collected new samples and measured fission track and (U‐Th)/He cooling ages of apatite and zircon from 13 Jurassic and Cretaceous granitoids in western Graham Land between the northern tip of the peninsula and the Antarctic Circle. Apatite He data reveal distinct ages and systematic age patterns north and south of Anvers Island, near the midpoint of the study area: To the south, apatite …
Detrital-Zircon Geochronology Of The Metasedimentary Rocks Of North-Western Graham Land, David Barbeau, Justin Davis, Kendra Murray, Victor Valencia, George Gehrels, Khandaker Zahid, David Gombosi
Detrital-Zircon Geochronology Of The Metasedimentary Rocks Of North-Western Graham Land, David Barbeau, Justin Davis, Kendra Murray, Victor Valencia, George Gehrels, Khandaker Zahid, David Gombosi
David L Barbeau Jr
Metasedimentary rocks constitute an important but comparatively poorly understood part of the Antarctic Peninsula. Herein we report single-grain U-Pb detrital-zircon ages from samples of the Trinity Peninsula and Botany Bay Groups of north-western Graham Land. All studied samples are dominated by a large and narrowly defined population of late Palaeozoic zircons. Significant early–middle Palaeozoic and minor Neoproterozoic and Mesoproterozoic sub-populations constitute the majority of pre-Carboniferous grains. These detrital-zircon age populations are consistent with sediment derivation entirely from western Gondwana sources. Despite the clear Gondwana signatures, our data suggest that the Trinity Peninsula Group province was either a parautochthonous peri-Gondwanan terrane …
Nearest Neighbor Methods Applied To Dune Field Organization: The Coral Pink Sand Dunes, Kane County, Utah, Usa, David Wilkins, Richard Ford
Nearest Neighbor Methods Applied To Dune Field Organization: The Coral Pink Sand Dunes, Kane County, Utah, Usa, David Wilkins, Richard Ford
David E. Wilkins
Dune fields have recently come to be recognized as self-organizing systems that can be seen progressing from states of disorganization or randomness to uniformity. Dune systems can be highly sensitive to changes in factors, such as climate and sediment transport, that determine system state. Changes in climate and sediment state can take time to work their way through a dune system; this, in turn, leads to spatial heterogeneity in dune field organization. Using the Coral Pink Sand Dunes in southern Utah as a model, this study tests nearest neighbor analysis adapted as a method to objectively identify and characterize differences …
Palaeolake Shoreline Sequencing Using Ground Penetrating Radar: Lake Alvord, Oregon, And Nevada, David Wilkins, William Clement
Palaeolake Shoreline Sequencing Using Ground Penetrating Radar: Lake Alvord, Oregon, And Nevada, David Wilkins, William Clement
David E. Wilkins
Field, map, and aerial photoreconnaissance in the Lake Alvord basin has focused on identifying late Pleistocene depositional shoreline features (e.g., tombolos, spits, barriers). Features in different areas of the basin are well defined, and their spatial extents are easily mapped; however, absolute---or even relative-ages of shoreline features are not clear. Ground penetrating radar (GPR) was used to distinguish between intermediate and highstand stage shorelines during what is thought to have been the latest Pleistocene, threshold-controlled lake cycle. Radar transects of 280 and 600 m imaged a spit and a baymouth barrier at sites in the northeastern quadrant of the basin …
Dating Of Major Normal Fault Systems Using Thermochronology: An Example From The Raft River Detachment, Basin And Range, Western United States, Michael Wells, Lawrence Snee, Ann Blythe
Dating Of Major Normal Fault Systems Using Thermochronology: An Example From The Raft River Detachment, Basin And Range, Western United States, Michael Wells, Lawrence Snee, Ann Blythe
Ann Blythe
Application of thermochronological techniques to major normal fault systems can resolve the timing of initiation and duration of extension, rates of motion on detachment faults, timing of ductile mylonite formation and passage of rocks through the crystal-plastic to brittle transition, and multiple events of extensional unroofing. Here we determine the above for the top-to-the-east Raft River detachment fault and shear zone by study of spatial gradients in 40Ar/39Ar and fission track cooling ages of footwall rocks and cooling histories and by comparison of cooling histories with deformation temperatures. Mica 40Ar/39Ar cooling ages indicate that extension-related cooling began at ∼25–20 Ma, …
Adaptation To Hard-Object Feeding In Sea Otters And Hominins, Paul Constantino, James Lee, Dylan Morris, Peter Lucas, Adam Hartstone-Rose, Wah-Keat Lee, Nathaniel Dominy, Andrew Cunningham, Mark Wagner, Brian Lawn
Adaptation To Hard-Object Feeding In Sea Otters And Hominins, Paul Constantino, James Lee, Dylan Morris, Peter Lucas, Adam Hartstone-Rose, Wah-Keat Lee, Nathaniel Dominy, Andrew Cunningham, Mark Wagner, Brian Lawn
Paul J. Constantino
The large, bunodont postcanine teeth in living sea otters (Enhydra lutris) have been likened to those of certain fossil hominins, particularly the ’robust’ australopiths (genus Paranthropus). We examine this evolutionary convergence by conducting fracture experiments on extracted molar teeth of sea otters and modern humans (Homo sapiens) to determine how load-bearing capacity relates to tooth morphology and enamel material properties. In situ optical microscopy and x-ray imaging during simulated occlusal loading reveal the nature of the fracture patterns. Explicit fracture relations are used to analyze the data and to extrapolate the results from humans to earlier hominins. It is shown …
When Will America, World Make Sustainability A Priority?, John Dernbach
When Will America, World Make Sustainability A Priority?, John Dernbach
John C. Dernbach
No abstract provided.
Sustaining America, John Dernbach
Sustaining America, John Dernbach
John C. Dernbach
This essay summarizes U.S. sustainability efforts over the two decades since the U.N. Conference on Environment and Development (or Earth Summit) in 1992. It also summarizes basic findings and recommendations from Acting as if Tomorrow Matters: Accelerating the Transition to Sustainability (Environmental Law Institute 2012). Drawing on the expertise of more than four dozen sustainability practitioners in a variety of fields, the book teases from the limited progress made in the United States over the past two decades the overall patterns for that progress. It also reviews the most significant obstacles to sustainability, again showing patterns in those obstacles across …
Constraints On Exhumation And Extensional Faulting In Southwestern Nevada And Eastern California, U.S.A., From Zircon And Apatite Thermochronology, David Ferrill, Alan Morris, John Stamatakos, Deborah Waiting, Raymond Donelick, Ann Blythe
Constraints On Exhumation And Extensional Faulting In Southwestern Nevada And Eastern California, U.S.A., From Zircon And Apatite Thermochronology, David Ferrill, Alan Morris, John Stamatakos, Deborah Waiting, Raymond Donelick, Ann Blythe
Ann Blythe
Eastern California and southwestern Nevada represent an area of Tertiary and Quaternary extensional and dextral transtensional deformation. We used zircon and apatite fission-track thermochronology to study the distribution and timing of tectonic exhumation resulting from extensional and transtensional detachment faulting in this area. Sampling efforts were focused on Paleozoic and Precambrian clastic sedimentary and metasedimentary rocks. Sixty-nine new apatite and zircon fission-track cooling ages from 50 samples, analyzed in conjunction with published fission-track data from the region, indicate a distinct population of young (Miocene) fission-track ages and a population of irregularly distributed older (pre-Miocene) fission-track ages. Miocene (young population) fission-track …
A New Eusuchian Crocodyliform With Novel Cranial Integument And Its Significance For The Origin And Evolution Of Crocodylia, Casey Holliday, Nicholas Gardner
A New Eusuchian Crocodyliform With Novel Cranial Integument And Its Significance For The Origin And Evolution Of Crocodylia, Casey Holliday, Nicholas Gardner
Nicholas Gardner
Crocodyliforms were one of the most successful groups of Mesozoic tetrapods, radiating into terrestrial, semiaquatic and marine environments, while occupying numerous trophic niches, including carnivorous, insectivorous, herbivorous, and piscivorous species. Among these taxa were the enigmatic, poorly represented flat-headed crocodyliforms from the late Cretaceous of northern Africa. Here we report a new, giant crocodyliform from the early Late Cretaceous (Cenomanian) Kem Kem Formation of Morocco. Represented by a partial braincase, the taxon has an extremely long, flat skull with large jaw and craniocervical muscles. The skull roof is ridged and ornamented with a broad, rough boss surrounded by significant vascular …
Sharks Of The Devonian, Andrew Blitman
Book Review: Biology Of The Sauropod Dinosaurs: Understanding The Lives Of Giants, Kristi Curry Rogers
Book Review: Biology Of The Sauropod Dinosaurs: Understanding The Lives Of Giants, Kristi Curry Rogers
Kristi Curry Rogers
No abstract provided.