1,721,026 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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The Late Quaternary Evolution of the Southern California Coast: Sea-Level Change, Storms, and Subsidence
Full text linkThe highly developed and populated coast of southern California is at risk for inundation due to storms or tsunamis; coastal erosion; wildfires; earthquake-driven shaking, liquefaction, and subsidence; sea-level rise; and other hazards. Estuaries formed during periods of sea-level transgressions often record environmental changes that have affected the region over time. These records of past climate, sea level, inundation events, and other changes can provide a baseline with which to compare current changes. Past recurrence intervals of hazard events also provide an estimate for how often and at what magnitude we can expect events to recur in the future. Here we compile relative sea-level indicators from other studies on southern California estuaries to show that relative sea level in southern California has risen 0.8 ± 0.3 mm/yr over the last 4000 years, less than modern rates and predicted future rates of sea-level rise. Predicted acceleration of sea-level rise could exacerbate the effects of storm and tsunami inundation along the coast. We use a variety of biological, sedimentological, and geochemical measurements on sediment cores from Carpinteria Marsh, Carpinteria, California, to document environmental changes that have occurred along the Santa Barbara Channel over the last 10,000 years. We show evidence for at least 37 episodes of alluvial fan progradation due to large floods over the past 7 ka, clusters of which correspond to regional records of wet climate conditions. We also show evidence for one coseismic subsidence event at 1.0 ± 0.1 ka, which may correlate with records of other earthquakes in the region. Finally, the topmost sediments within the marsh record environmental changes within the historical period. Within these sediments, we use a multi-proxy approach to document the history of the marsh over the last 200 years including the appearance of European pollen species, makers of industrialization, and an overwash deposit related to the 1861-2 winter storm season in California
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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Recording Coastal Changes observed in Beach Ridges and Prograded Beach Stratigraphy using Ground-Penetrating Radar
Full text linkBeach ridges and other prograding beach deposits are important sedimentary archives of past floods, storms, and relative sea-level changes. Accurate interpretations of beach ridges requires an understanding of their formation and preservation through time. In the following studies, I use ground-penetrating radar to observe the stratigraphy of beach ridges and prograded beach deposits. Additionally, I employ the use of elevation surveys, aerial photographs, radiocarbon dating, and optically stimulated luminescence dating to understand the timing of events preserved in the sedimentary record. In Chapter 2, I explore the formation of swash bars on the Elwha River delta after the removal of two dams on the fluvial system simulated a large sediment pulse to the system, similar to a flood or landslide. I find that mouth bars form most often after higher than average discharge events in the fluvial system, and swash bars form soon after due to wave reworking of the mouth-bar sediments. However, only 10 of 37 swash bars that formed were preserved at the time of my GPR survey, five years after dam removal. Additionally, the swash bars that did survive amalgamated with one another, forming a large barrier at the delta front, indicating that in small mountainous river settings, beach ridges may be more indicative a large sediment pulse to the system, rather than a single flood. In Chapter 3, I examine the ~600-year sedimentary record of the coastal Oxnard Plain. Progradation on the Oxnard Plain has been relatively constant on centennial (150- to 200-year) timescales, prograding at rates of 0.3 to 1.4 m a-1. However, on shorter timescales, progradation is episodic, with greater progradation occurring after high discharge events along the Santa Clara River. Extended droughts remove up to 90 m of the beach, equivalent to ~5 to ~120 years of the sedimentary record. Additionally, I image beach cusps in shore parallel GPR profiles, which previously had not been recognized in GPR profiles.Lastly, in Chapter 4 I use gravel beach ridges to reconstruct the relative sea-level (RSL) record on Joinville Island, Antarctica. I find that RSL has fallen ~5 m over the last ~3000 years, at variable rates throughout the late Holocene. I interpret that ice mass loss, similar to the scale of ice mass loss after the 2002 Larsen B Ice shelf collapse, and ice mass growth caused by glacial advance, both occurred in the Late Holocene and were recorded in my RSL reconstruction. Therefore, global- and continental-scale global isostatic adjustment models, which currently only account for ice changes on thousand-year timescales, are missing crucial centennial-timescales ice mass changes
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Sea-level records and processes operating on California shelves: Past and present
No full textContinental shelves have long been conceptualized as sediment-starved, relict landscapes shaped by past sea-level fluctuations and marked by drowned coastal features. This view, however, overlooks the dynamic nature of these environments, particularly along mid-latitude transgressed margins like the central California shelf. These environments not only archive sea-level history but also host sedimentary processes that shape and maintain geomorphic features, including subaqueous clinoforms. This dissertation investigates the interplay between relative sea-level (RSL) change and shelf morphodynamics from the Late Pleistocene to the Eocene, with a particular focus on the formation, preservation, and stratigraphic architecture of subaqueous clinoforms.The study is structured around three studies that span, Holocene, Late Pleistocene and ancient geologic contexts. Chapter 2 develops a novel methodology to reconstruct post-Last Glacial Maximum (LGM) RSL along the central California shelf. Using sediment cores, high-resolution seismic data, and modern wave data, the study develops two new sea-level indicators: the Wave Ravinement Shell Hash Burial Surface (WRSHBS) and the contact between an inner shelf sand and an offshore mud. These indicators were used to produce the earliest post-LGM RSL constraints for California, extending that record back to 13.8–15.5 cal ka BP, at which time sea level was between 86 ± 8 and 99 ± 8 m below present. Additional constraints from the contact between an inner shelf sand and an offshore mud provide RSL estimates between 37 ± 7.5 and 49 ± 7.5 m below present between ~9 and ~12 ka BP. This method allows sea-level reconstructions to be extended into a period previously lacking data along much of the globe’s mid-latitude shelves.Chapter 3 documents the progradation of a Holocene sandy subaqueous clinoform along the central California shelf, known as the Cross Hosgri Slope. Sediment cores, chirp sub-bottom profiles, and radiocarbon dating reveal that clinoform initiation began shortly after sea level stabilized following the LGM, with progradation beginning between approximately 8.3 and 7.2 cal ka BP. The clinoform is not directly sourced by fluvial input, but instead by winter swell waves that remobilize shelf sands into wave-supported sediment gravity flows. These flows deposited decimeter-scale coarsening-upward sedimentary successions characterized by ripple cross-lamination and parallel lamination, which record the waxing and waning of turbulent flow transport. This chapter presents a new facies model for sandy subaqueous clinoforms formed in isolation and demonstrates that these features can accumulate in high-energy shelf settings without river-derived sediment. This study offers new criteria for identifying sandy subaqueous clinoforms and presents tools to distinguish them from lowstand shoreline deposits, helping prevent their misinterpretation in RSL and paleogeographic reconstructions.Chapter 4 shifts to an ancient example of a shelfal clinoform: a compound delta-scale clinoform preserved in the middle Eocene Cozy Dell Formation of southern California. Measured sections, facies analysis, and detrital zircon geochronology reveal a stratigraphic architecture strikingly similar to modern compound clinoforms. The subaqueousc clinoform in the informal Nordoff sandstone of the Cozy Dell formation records a progression from distal hyperpycnite beds to proximal storm-influenced foresets, while the overlying Circle B Sandstone represents the subaerial delta front. Paleocurrent indicators suggest sediment was delivered from the southeast and redistributed along and across the shelf by wave-supported and shore-parallel currents. This sandstone member represents a rare stratigraphic link between subaerial delta deposits and their subaqueous clinoform counterparts.Collectively, these studies demonstrate that subaqueous clinoforms are underrecognized in both modern and ancient records, and are frequently misinterpreted as paleoshorelines—an error that can significantly affect sea-level and paleogeographic reconstructions. This dissertation presents new tools and facies models for identifying and interpreting clinoform deposits, emphasizing their importance as active sedimentary bodies
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Antarctic raised beaches: Insight on geochronology, relative sea level, and coastal processes
Full text linkBeaches are preserved above sea level along ice-free portions of the Antarctic coastline due to post-glacial rebound associated with glacial isostatic adjustment since the Last Glacial Maximum. The ages and elevations of these beaches provide relative sea-level constraints for glacial isostatic adjustment models and ice-sheet histories. Due to harsh field conditions and difficulty dating Antarctic materials, a lack of geochronological constraints on raised beaches limits our understanding of relative sea level around Antarctica. The focus of the studies discussed here is on Antarctic raised beaches with goals to improve the methods of dating cobble surfaces from raised beaches using optically stimulated luminescence and use the dated beaches to reconstruct relative sea level and better understand Antarctic coastal processes throughout the Holocene. Through a series of cleaning methods applied to sample carriers used for optically stimulated luminescence measurements of sediment, the contamination of dose-dependent, variable signals from sample carriers previously assumed to have neutral signals is eliminated through a series of cleaning methods (Chapter 2). An analysis of optically stimulated luminescence characteristics of quartz from cobble surfaces with sample petrology and cathodoluminescence provides insight on the suitability of Antarctic materials for optically stimulated luminescence dating (Chapter 3). The limited amount of quartz (<10%) found in the majority of the samples often occurs as intergrowths in feldspars characterized by irregular, anhedral crystal form. A lack of discernible relationship between optically stimulated luminescence and cathodoluminescence properties and petrology suggest that cathodoluminescence behavior and petrology are not responsible for the poor luminescence characteristics observed from quartz extracted from cobble surfaces. A relative sea-level history of Marguerite Bay, Antarctic Peninsula derived from optically stimulated luminescence-dated beach cobble surfaces further constrains post-glacial rebound since the Last Glacial Maximum (Chapter 4). New ages suggest the Holocene marine limit for Marguerite Bay is 21.7 masl with an age of ~ 5.5-7.3 ka. Our favored hypothesis for the ages of the beaches from 21.7-40.8 masl at Calmette Bay is that the beaches formed prior to the Last Glacial Maximum. The temporal distribution of circum-Antarctic raised beaches throughout the Holocene is utilized to determine the relationship between wave-energy, sea ice, and coastal evolution (Chapter 5). The distribution of raised beaches throughout the Holocene around Antarctica show synchronous periods of beach formation in the Antarctic Peninsula and the Ross Sea centered at 2.0, 3.5, and 5.3 ky BP while East Antarctic (outside of the Ross Sea) beach formation is out-of-phase with the rest of the Antarctica at 3.2, 4.2, 5.8, and 6.5 ky BP. The distribution of beaches in the South Shetland Islands is dominated by enhanced beach formation between 0.2 and 0.7 ky BP most likely due to rapid post-glacial rebound associated with the Little Ice Age with minor peaks in beach formation from 1.3-2.2, 5.1-5.6, and 6.0-6.5 ky BP. Beach formation results from higher wave exposure during periods of reduced sea ice observed from comparison with Holocene sea-ice proxies. The anti-phasing of beach formation in the Antarctic Peninsula and Ross Sea compared to East Antarctica is markedly similar to the phasing of modern and Holocene climate forcing around Antarctica. The findings of these studies focused on Antarctic raised beaches have implications for understanding sea-level, glacial isostatic adjustment, ice-sheet histories, and coastal processes since the Last Glacial Maximum.
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Age, Provenance, and Facies Architecture of an arid-land fluvial system in equatorial Pangaea: The Cloud Chief Formation in western Oklahoma, U.S.A.
Full text linkThe Permian redbeds of the Midcontinent U.S.A. are thought to contain important clues to the climate history of western Pangaea. However, before these units can be used as paleoclimatic archives, better constraints are needed on their age, depositional environment, and provenance. In this study, 43 stratigraphic sections were measured within the Lopingian Cloud Chief Formation of western Oklahoma. The sections were complemented by strontium isotope analysis and detrital zircon geochronology. Nine facies were recognized within the measured sections. These facies include massive gypsum, gypsiferous sandstones, channelized very fine sandstones, thickly-bedded sandstones, siltstones, variegated mudstones, ripple cross-laminated very fine sandstones, interbedded sandstones and mudstones, and silty claystones. These facies are interpreted to represent subenvironments of widespread arid-land fluvial systems flowing into a sabkha. These interpretations fit well with other recent work calling for arid conditions within the midcontinent during the middle Permian. Detrital zircon geochronology points to a dominant sediment source to the east (Ouachita Mountains) with a subordinate source to the west (Ancestral Rocky Mountains in Colorado and New Mexico). Strontium isotope values of the massive gypsum facies provide evidence for marine encroachment during periods of high relative sea level. These isotope values point to an age for the Cloud Chief of 262 ± 3 Ma to 255 ± 3 Ma, providing some of the first numerical ages from the redbeds of western Oklahoma
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Insights into the Sea-Level History of the South Shetland Islands from Ground Penetrating Radar on Livingston Island, Antarctica
Full text linkRaised beach ridges in polar environments are recorders of relative sea-level (RSL) change. The South Shetland Islands (SSI) contain large areas of ice-free raised beaches used to resolve paleo-sea-level change. The largest of these ice-free areas is Byers Peninsula (60 km2) on Livingston Island, SSI. This peninsula and other ice-free coasts within the SSI contain series of raised beach ridges correlated by age and elevation. The internal architecture of these beach ridges is critical to understanding paleo-RSL. The non-destructive method of ground penetrating radar (GPR) was used to investigate the internal architecture of the South Beaches of Livingston Island where a flight of nine beach ridges (five of which were the focus of in this study) have been glacio-isostatically raised since the last glacial maximum (LGM). Recalibrated radiocarbon ages collected from these and other beach ridges in previous studies are used to relate beach morphology and stratigraphy to the glacial history of the region. Over 10 km of 200 MHz GPR transects and synchronous GPS were collected over a two-week period in the spring of 2019. Sediment pits <1 m in depth were dug to search for dateable material and described for ground truthing of GPR reflections. Six key radar facies and three radar surfaces were identified: a seaward dipping progradational facies, a landward dipping overwash facies, a flat and concave down aggradational facies, a discontinuous hyperbola rich cobble facies, a flat lying lagoon facies, and a channelized fluvial facies. Erosional and toplapping surfaces were identified in addition to the top of the bedrock. Within this flight of raised beach ridges evidence was found of transgressive depositional patterns marked by progradational seaward dipping facies deposited during periods of RSL fall followed by erosion and overlying deposition of landward dipping overwash and aggrading beds. This succession is routinely located over a notch in the bedrock interpreted to represent a wave-cut feature. An apparent correlation between the ages of beach ridges and wave-cut notches with known neoglacial advances at ~5.5 ka, ~3-1 ka, and ~0.4 ka suggests that the influence of glacial-isostatic adjustment (GIA) on RSL is responsible for the origin of the beach ridges and the underlying wave-cut scarps. This GIA hypothesis further supports recent assertions of a much more dynamic RSL history for Antarctic coastlines, which may “contaminate” the LGM RSL signal across Antarctica
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