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Search Results: 1 - 10 of 2216 matches for " Carr; Swisher III "
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Progress and Challenges Using 40Ar/39Ar Geochronology in Costa Rica and Nicaragua
Saginor1,Ian; Gazel,Esteban; Michael J,Carr; Swisher III,Carl C; Turrin,Brent;
Revista Geológica de América Central , 2011,
Abstract: to better estimate the extrusive flux of the central american arc, from 2002-2008, we obtained sixty one high precision 40ar/39ar ages on geographically well-situated lavas and tephra from costa rica and nicaragua. here, we describe a number of observations encountered during this study using four examples that well document the precision, accuracy and general reliability of the 40ar/39ar ages. first, low k2o values, particularly in samples from nicaragua, is a major limitation in or attempts to obtain reliable dates on samples under 1 my. second, extensive weathering of samples due to the tropical climate of central america has resulted in various levels of argon loss even when the hand sample appeared unaltered. third, our field and geochronological data lead us to conclude that eruptive rates have not been constant over the past 15 to 20 my, but rather appears punctuated by gaps of up to several million years. we attempted to address the temporal gaps in several ways. first, geochemical analyses were used to identify samples that may have erupted during time periods without known volcanism. for example, u/th values in the active central american arc are significantly higher than those obtained from the miocene coyol group except for four samples with intermediate values that were dated to determine if their ages were intermediate as well. however, all of these samples were found to be from a period with known volcanism. second, we sought to locate the oldest sections of the active arc and the youngest sections of the coyol group in order to better constrain the timing and duration of the apparent gap in volcanic productivity. this approach also failed to locate samples from periods without known volcanism. when these methods proved largely unsuccessful, our focus shifted to dating regions of minor volcanism between the active and coyol volcanic fronts as well as between cosigüina and san cristóbal, the longest stretch of the central american volcanic front withou
Progreso y retos de la geocronología 40Ar/39Ar en Costa Rica y Nicaragua Progress and Challenges Using 40Ar/39Ar Geochronology in Costa Rica and Nicaragua
Ian Saginor1,Esteban Gazel,Carr Michael J,Carl C Swisher III
Revista Geológica de América Central , 2011,
Abstract: Con el principal objetivo de realizar mejores cálculos de la producción volcánica, en el Arco Volcánico de América Central, realizamos 61 dataciones 40Ar/39Ar en tefras y lavas en localidades de frente volcánico de Costa Rica y Nicaragua por medio de varias campa as de campo y análisis de laboratorio (preparación de muestras, envió al reactor nuclear, espectroscopía de masas de las muestras radiactivas, al laboratorio de gases nobles del Departamento de Ciencias de la Tierra y Planetarias de la Universidad Rutgers) del 2002-2008. En este artículo presentamos diferentes observaciones que resultaron de este estudio donde se describe la precisión, exactitud y la confiabilidad de las edades 40Ar/39Ar. El primer resultado muestra las limitaciones de esta técnica en muestras baja en K2O con edades < 1 Ma, especialmente en Nicaragua. El segundo resultado muestra los efectos de la pérdida de Ar por los procesos de meteorización típicos del trópico, inclusive afectando las muestras sanas a nivel críptico. El tercer resultado sugiere que las razones eruptivas del frente volcánico no han sido constantes durante los últimos 15-20 Ma, sino más bien representan ciclos eruptivos. Con el propósito de evaluar los hitos entre diferentes ciclos eruptivos, evaluamos los datos geoquímicos a lo largo del frente volcánico, en especial las relaciones U/Th, cuyos valores son inferiores (Grupo Coyol) en Nicaragua, comparados con el frente volcánico activo. Sin embargo, las muestras seleccionadas con base en geoquímica, resultaron ser de edades conocidas y no produjeron datos que llenan los hiatos entre ciclos de actividad volcánica. La siguiente estrategia que manejamos fue extender el muestreo en el Grupo Coyol, inmediatamente detrás del frente volcánico activo, sin embargo, esta estrategia no fue exitosa para encontrar muestras que llenaran los hiatos de actividad. No obstante, obtuvimos edades de 1.1-3,6 Ma entre los volcanes Cosiguina and San Cristóbal, los cuales limitan el hiato de actividad y mejoran nuestra percepción de los ciclos de actividad volcánica en América Central. To better estimate the extrusive flux of the Central American Arc, from 2002-2008, we obtained sixty one high precision 40Ar/39Ar ages on geographically well-situated lavas and tephra from Costa Rica and Nicaragua. Here, we describe a number of observations encountered during this study using four examples that well document the precision, accuracy and general reliability of the 40Ar/39Ar ages. First, low K2O values, particularly in samples from Nicaragua, is a major limitation in or attempts to obtain
On the supercongruence conjectures of van Hamme
Holly Swisher
Mathematics , 2015,
Abstract: In 1997, van Hamme developed $p-$adic analogs, for primes $p$, of several series which relate hypergeometric series to values of the gamma function, originally studied by Ramanujan. These analogs relate truncated sums of hypergeometric series to values of the $p-$adic gamma function, and are called Ramanujan type supercongruences. In all, van Hamme conjectured 13 such formulas, three of which were proved by van Hamme himself, and five others have been proved recently using a wide range of methods. Here, we explore four of the remaining five van Hamme supercongruences, revisit some of the proved ones, and provide some extensions.
HALO: Report and Predicted Response Times
Matthew Swisher
Computer Science , 2015,
Abstract: HALO: Heterogeneity-Aware Load Balancing is a paper that proposes a class of heterogeneity-aware Load Balancers (LBs) for cluster systems. LBs that are heterogeneity-aware are able to detect when servers differ in speeds and in number of cores. Response times for heterogeneous systems are calculated and presented.
Further support for a Cretaceous age for the feathered-dinosaur beds of Liaoning, China: New 40Ar/39Ar dating of the Yixian and Tuchengzi

C C Swisher III,WANG Xiaolin,ZHOU Zhonghe,WANG Yuanqing,JIN Fan,ZHANG Jiangyong,XU Xing,ZHANG Fucheng,WANG Yuan,

科学通报(英文版) , 2002,
Abstract: We report new 40Ar/39Ar dating results obtained from total fusion and incremental-heating analyses of sanidine and biotite from three tuffs found interbedded within the fossil-bearing deposits of Liaoning, northeast China. The first is a new sample of the Bed 6 Sihetun tuff from the Yixian Formation, previously dated by our team as middle Early Cretaceous, and recently considered by Lo et al., partially reset due to metamorphism from a nearby basaltic sill. The second is the Yixian Bed 9 tuff from Hengdaozi considered by Lo et al. to be unaffected by metamorphism and whose age, based on total fusion 40Ar/39Ar dating of biotite, argues for a Jurassic age for the Yixian Formation. The third tuff is a previously undated tuff from the upper part of the underlying Tuchengzi Formation. Single crystal total fusion 40Ar/39Ar analyses of the Sihetun sanidine showed homogeneous radiogenic Ar, Ca/K ratios, excellent reproducibility and gave a mean age of 125.0 ± 0.18 (1SD) ± 0.04 (SE) Ma. Single sanidine crystal total fusion 40Ar/39Ar analyses of the Hengdaozi tuff gave a mean age of 125.0 ± 0.19 (1SD) ± 0.04 (SE) Ma, which is indistinguishable from the Sihetun tuff. The Tuchengzi Formation tuff gave a mean age of 139.4 ± 0.19 (1SD) ± 0.05 (SE) Ma. Detailed laser incremental-heating analyses of biotite from Sihetun, Hengdaozi, and Tuchengzi tuffs show disturbed Ar release patterns and evidence of trapped argon components. We conclude from these analyses that the total fusion dates on biotite by Lo et al. are erroneously old and isotopic dating of both biotite and sanidine from tuffs of the Yixian Formation point to a middle Early Cretaceous age. The upper part of the Tuchengzi Formation can be referred to the Early Cretaceous.
The Age of the 20 Meter Solo River Terrace, Java, Indonesia and the Survival of Homo erectus in Asia
Etty Indriati,Carl C. Swisher III,Christopher Lepre,Rhonda L. Quinn,Rusyad A. Suriyanto,Agus T. Hascaryo,Rainer Grün,Craig S. Feibel,Briana L. Pobiner,Maxime Aubert,Wendy Lees,Susan C. Antón
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0021562
Abstract: Homo erectus was the first human lineage to disperse widely throughout the Old World, the only hominin in Asia through much of the Pleistocene, and was likely ancestral to H. sapiens. The demise of this taxon remains obscure because of uncertainties regarding the geological age of its youngest populations. In 1996, some of us co-published electron spin resonance (ESR) and uranium series (U-series) results indicating an age as young as 35–50 ka for the late H. erectus sites of Ngandong and Sambungmacan and the faunal site of Jigar (Indonesia). If correct, these ages favor an African origin for recent humans who would overlap with H. erectus in time and space. Here, we report 40Ar/39Ar incremental heating analyses and new ESR/U-series age estimates from the “20 m terrace" at Ngandong and Jigar. Both data sets are internally consistent and provide no evidence for reworking, yet they are inconsistent with one another. The 40Ar/39Ar analyses give an average age of 546±12 ka (sd±5 se) for both sites, the first reliable radiometric indications of a middle Pleistocene component for the terrace. Given the technical accuracy and consistency of the analyses, the argon ages represent either the actual age or the maximum age for the terrace and are significantly older than previous estimates. Most of the ESR/U-series results are older as well, but the oldest that meets all modeling criteria is 143 ka+20/?17. Most samples indicated leaching of uranium and likely represent either the actual or the minimum age of the terrace. Given known sources of error, the U-series results could be consistent with a middle Pleistocene age. However, the ESR and 40Ar/39Ar ages preclude one another. Regardless, the age of the sites and hominins is at least bracketed between these estimates and is older than currently accepted.
Interactions between Upf1 and the Decapping Factors Edc3 and Pat1 in Saccharomyces cerevisiae
Kylie D. Swisher, Roy Parker
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0026547
Abstract: In Saccharomyces cerevisiae, mRNA transcripts with premature termination codons are targeted for deadenylation independent decapping and 5′ to 3′ decay in a quality control pathway termed nonsense-mediated decay (NMD). Critical factors in NMD include Upf1, Upf2, and Upf3, as well as the decapping enzyme, Dcp2/Dcp1. Loss of Upf2 or Upf3 leads to the accumulation of not only Upf1 and Dcp2 in P-bodies, but also of the decapping-activators Pat1, Dhh1, and Lsm1. An interaction between Upf1 and Dcp2 has been identified, which might recruit Dcp2 to the NMD decapping complex. To determine the nature and significance of the Dcp2-Upf1 interaction, we utilized the yeast two-hybrid assay to assess Upf1 interactions with various mRNA decapping factors. We find that although Dcp2 can interact with Upf1, this interaction is indirect and is largely dependent on the Edc3 protein, which interacts with the N-terminal domain of Upf1 at an overlapping, but not identical, site as Upf2. We also found that Pat1 has an independent two-hybrid interaction with the N-terminus of Upf1. Assessment of both reporter and endogenous NMD transcripts suggest that the decapping stimulators, including Edc3 and Pat1, as well as Edc1 and Edc2, are not essential for NMD under normal conditions. This work defines a larger decapping complex involved in NMD, but indicates that components of that complex are not required for general NMD and might either regulate a subset of NMD transcripts or be essential for proper NMD under different environmental conditions.
Localization to, and Effects of Pbp1, Pbp4, Lsm12, Dhh1, and Pab1 on Stress Granules in Saccharomyces cerevisiae
Kylie D. Swisher,Roy Parker
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0010006
Abstract: The regulation of translation and mRNA degradation in eukaryotic cells involves the formation of cytoplasmic mRNP granules referred to as P-bodies and stress granules. The yeast Pbp1 protein and its mammalian ortholog, Ataxin-2, localize to stress granules and promote their formation. In Saccharomyces cerevisiae, Pbp1 also interacts with the Pab1, Lsm12, Pbp4, and Dhh1 proteins. In this work, we determined whether these Pbp1 interacting proteins also accumulated in stress granules and/or could affect their formation. These experiments revealed the following observations. First, the Lsm12, Pbp4, and Dhh1 proteins all accumulate in stress granules, whereas only the Dhh1 protein is a constitutive P-body component. Second, deletion or over-expression of the Pbp4 and Lsm12 proteins did not dramatically affect the formation of stress granules or P-bodies. In contrast, Pbp1 and Dhh1 over-expression inhibits cell growth, and for Dhh1, leads to the accumulation of stress granules. Finally, a strain lacking the Pab1 protein was reduced at forming stress granules, although they could still be detected. This indicates that Pab1 affects, but is not absolutely required for, stress granule formation. These observations offer new insight into the function of stress granule components with roles in stress granule assembly and mRNP regulation.
A Pilot Study on the New USDA Meal Pattern for School Breakfast in a Sample of First-Grade Students  [PDF]
Noelle Carr, Sibylle Kranz
Food and Nutrition Sciences (FNS) , 2012, DOI: 10.4236/fns.2012.39175
Abstract: Background: The United States Department of Agriculture (USDA) recently modified the school breakfast program (SBP) to improve children’s nutrition. Based on the new patterns, schools must offer larger amounts of fruits, grains, and proteins/meats to children; the amounts of fluid foods (milk and juice) remained the same. This study examined the effect of the new food pattern on student’s consumption and food cost. Methods: The amounts and cost of foods served and wasted for one week in first grade students attending two elementary schools (n = 812) were measured. One school received the current SBP pattern (control breakfast, average number of students attending breakfast n = 81), the other school’s breakfast reflected the proposed changes (test breakfast, n = 82). To test the hypothesis that the test breakfast leads to significantly increased food cost and food waste compared to the control breakfast, the weekly average amount of the served solid and fluid foods (grams and milliliters) as well as their waste were compared between the two groups using paired student’s t-test in STATA 11 (significance at p-value < 0.05). Results: Data confirmed the hypothesis in that the test breakfast was associated with significantly higher food cost (by approximately $100/week) and solid food waste but there was no change in milk and juice consumption. Conclusions: This exploratory study indicates that a significant portion of the additional foods served to first-graders to improve their nutritional status were not consumed but wasted. Further studies in larger samples and including students from all grades are needed to examine this issue fully.
Weather extremes from anthropogenic global warming  [PDF]
Paul H. Carr
Natural Science (NS) , 2013, DOI: 10.4236/ns.2013.51A020
Abstract:

Although sea levels are predicted to rise 1 to 2 meters by 2100, the more immediate effects of global warming are weather extremes. The number of natural disasters since 1996 costing $1 billion or more doubled compared with the previous 15-year period. Extreme summer heat anomalies now cover about 10% of land area, up from 0.2% in 1950-1980. The human influence on global warming is evident from climate data and physical modeling. Since the beginning of the industrial era, carbon dioxide (CO2) increases correlate with those of temperature. Carbon dating shows that the CO2 increase is from burning ancient fossil fuels. Increasing CO2 and other greenhouse gases blanket and warm the earth’s surface, allowing less heat to reach the stratosphere, which is cooling. This is consistent with satellite measurements showing that solar irradiance is not changing. The present CO2 rate increase of 2 ppm/year is 300 times higher than the rate at which the earth recovered from the ice age 18,000 years ago. Without the radiative forcing of noncondensing persistent CO2, the terrestrial greenhouse would collapse, plunging the global climate into an icebound earth state. Will new technologies lower our carbon emissions in time to prevent more weather extremes? Electric cars now get the equivalent of 100 miles per gallon. The cost of electricity from solar photovoltaic cells has reached grid parity.

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