scholarly journals Ultra-Microscale (5–25 μg C) Analysis of Individual Lipids by 14C AMS: Assessment and Correction for Sample Processing Blanks

Radiocarbon ◽  
2007 ◽  
Vol 49 (1) ◽  
pp. 69-82 ◽  
Author(s):  
Sunita R Shah ◽  
Ann Pearson
Keyword(s):  
Water Column ◽  
Euphotic Zone ◽  
Total Sample ◽  
Small Sample ◽  
Sample Processing ◽  
Central Pacific ◽  
The North ◽  
Pure Compounds ◽  
Small Sample Sizes ◽  
Different Sources

Measurements of the natural abundance of radiocarbon in biomarker molecules can be used to elucidate the biogeochemical roles of marine bacteria and archaea in the oceanic water column. However, the relatively low concentration of biomass, especially below the euphotic zone, inevitably results in small sample sizes for compound-specific analyses. In ultra-microscale Δ14C measurements, which we define as measurements on samples smaller than 25 μg C, the process of isolating pure compounds and preparing them for measurement adds significant background carbon. This additional blank carbon can contribute up to 40% of the total sample mass; therefore, it is necessary to quantify all components of the processing blank in order to make appropriate corrections. Complete propagation of error is critical in order to report the correct analytical uncertainty. The carbon blank is composed of at least 3 different sources: i) those that scale in proportion to the mass of the sample; ii) sources that contribute a constant mass of blank, e.g. closed-tube combustion; and iii) contaminants from vacuum lines and/or other aspects of sample handling that are difficult to quantify. We approached the problem of correcting for the total sample processing blank by deriving a 4-part isotopic mass balance based on separating the 3 exogenous components from the sample. Subsequently, we derived the appropriate equations for the full propagation of error associated with these corrections. Equations for these terms are presented. Full treatment of a set of raw data is demonstrated using compound-specific Δ14C data from the North Central Pacific water column.

scholarly journals Clonality in Sclerotinia sclerotiorum on Infected Cabbage in Eastern North Carolina

1997 ◽  
Vol 87 (10) ◽  
pp. 1000-1004 ◽  
Author(s):  
M. A. Cubeta ◽  
B. R. Cody ◽  
Y. Kohli ◽  
L. M. Kohn
Keyword(s):  
North Carolina ◽  
Sclerotinia Sclerotiorum ◽  
Total Sample ◽  
Small Sample ◽  
Dna Fingerprint ◽  
Dna Fingerprints ◽  
The North ◽  
Mycelial Compatibility ◽  
Eastern North Carolina ◽  
Two Populations

Eighty-four isolates of Sclerotinia sclerotiorum from four cabbage production fields in North Carolina and 16 isolates from an experimental cabbage field plot in Louisiana were DNA-fingerprinted and tested for mycelial compatibility. In a comparison with 594 unique DNA fingerprints of S. sclerotiorum from Canadian canola, no fingerprints were shared among Canadian, North Carolina, and Louisiana populations. DNA fingerprints from the North Carolina sample were distinctive from those of the Canadian and Louisiana samples, with significantly more hybridizing fragments in the 7.7- to 18-kilobase range. Forty-one mycelial compatibility groups (MCGs) and 50 unique DNA fingerprints were identified from the North Carolina sample. Three MCGs and three fingerprints were identified from the Louisiana sample. From the North Carolina sample, 32 MCGs were each associated with a unique fingerprint; of these, there were 11 clones (i.e., cases in which two or more isolates belonged to the same MCG and shared the same DNA fingerprint). Six clones sampled from two or more fields represented approximately 29% of the total sample (24 of 84 isolates), with six clones recovered from fields 75 km apart. There were 10 cases in which one MCG was associated with more than one DNA fingerprint and two cases in which one DNA fingerprint was associated with more than one MCG. The small sample from Louisiana was strictly clonal. The North Carolina sample had a clonal component, but deviated from one-to-one association of MCG with DNA fingerprint to an extent consistent with more recombination or transposition than the other two populations sampled.

Evaluating change in mobility in people with multiple sclerosis: relative responsiveness of four clinical measures

2013 ◽  
Vol 19 (12) ◽  
pp. 1632-1639 ◽  
Author(s):  
Jennifer Freeman ◽  
Richard Walters ◽  
Wendy Ingram ◽  
Anita Slade ◽  
Jeremy Hobart ◽  
...  
Keyword(s):  
Multiple Sclerosis ◽  
Community Sample ◽  
Total Sample ◽  
Small Sample ◽  
Change Scores ◽  
Study Results ◽  
Walking Velocity ◽  
Clinically Significant ◽  
Small Sample Sizes ◽  
Clinical Measures

Background and objectives: Determining responsiveness of measures across different samples and settings is important for selecting measures of mobility and understanding multiple sclerosis (MS) study results. Currently such information is limited. Methods: This exploratory study examined the relative responsiveness of four mobility measures (walking velocity, 6-minute walk distance, Rivermead Mobility Index and MS Walking Scale) in a community sample ( n = 70), after three annual assessments. Distribution based estimates and anchor-based methods (comparison against transition questions) determined responsiveness. A head-to-head comparison was made. Results: While variations in individuals occurred, the group mean change scores for all measures was small, suggesting that there was minimal deterioration in the total sample. Consistent with this, total sample Effect Size (ES) was negligible to small (ES −0.32 to +0.03) for all measures. Differentiation between sub-groups, defined by the participants’ perception of change in mobility over the past year (transition questions), showed that some instruments could detect clinically significant changes (small sample sizes limited this interpretation). Correlation analyses between change scores demonstrated that these measures captured related, but different information ( r < 0.364). Conclusions: The measures were broadly comparable in detecting mobility changes in this community sample. These correlations highlight that in selection of measures, one should also consider the discrete mobility dimension that the intervention intends to impact.

A small dasyurid predator (Sminthopsis virginiae) rapidly learns to avoid a toxic invader

2011 ◽  
Vol 38 (8) ◽  
pp. 726 ◽  
Author(s):  
Jonathan K. Webb ◽  
David Pearson ◽  
Richard Shine
Keyword(s):  
Western Australia ◽  
Small Sample ◽  
Ecological Impacts ◽  
Population Declines ◽  
Cane Toad ◽  
Taste Aversion Learning ◽  
The North ◽  
Formidable Challenge ◽  
Mammalian Predators ◽  
Small Sample Sizes

Context Invasive species are a leading cause of extinctions, yet predicting their ecological impacts poses a formidable challenge for conservation biologists. When native predators are naïve to invaders, they may lack appropriate behaviours to deal with the invader. In northern Australia, the invasion of the highly toxic cane toad (Rhinella marina) has caused serious population declines of reptilian and mammalian predators that are ill equipped to deal with toad toxins. Cane toads recently invaded the Kimberley region of Western Australia, where they potentially threaten several species of small dasyurid predators. Aims We investigated whether red-cheeked dunnarts (Sminthopsis virginiae) attack cane toads, and if so, whether individuals subsequently learn to avoid toads as prey. Methods We quantified feeding and learning behaviours in toad-naïve red-cheeked dunnarts from the north Kimberley in Western Australia. Key results All toad-naïve dunnarts attacked toads during their first encounter. Most dunnarts bit the toad on the snout, killed it by biting the cranium, and consumed the toad snout-first, thereby initially avoiding the toad’s parotoid glands. Most dunnarts partially consumed toads before discarding them, and only one animal showed visible signs of toad poisoning. All dunnarts rapidly learnt to avoid toads as prey after one or two encounters. Predators rejected toads as prey for the duration of the study (22 days), suggesting long-term retention of the knowledge that toads are noxious. Conclusions Our results show that red-cheeked dunnarts rapidly learn to avoid cane toads as prey. Implications Our study was limited by small sample sizes, but our results suggest that small dasyurids can adapt to the cane toad invasion via taste aversion learning.

Comparison of the Mantel-Haenszel Test With a Randomized and a Jackknife Test for Detecting Biased Items

1990 ◽  
Vol 15 (1) ◽  
pp. 53-67 ◽  
Author(s):  
Gregory Camilli ◽  
Jeffrey K. Smith
Keyword(s):  
Total Sample ◽  
Randomization Test ◽  
Small Sample ◽  
Reference Groups ◽  
Chi Square ◽  
Jackknife Test ◽  
Significance Levels ◽  
Chi Square Test ◽  
Small Sample Sizes ◽  
Haenszel Test

The Mantel-Haenszel (MH) chi-square test has been shown to have desirable statistical properties in detecting biased items. However, small sample sizes are still of concern, especially when large differences in ability exist between the focal and reference groups. This is because the accuracy and power of the MH test depends on the range of overlap between the focal and reference groups on raw scores, as well as the total sample size at any particular raw score. The MH procedure is compared with (a) a randomization test and (b) a jackknife test, which make weaker distributional assumptions. The MH chi-square significance levels were found to be extremely robust.

scholarly journals Evaluation of the seasonal formation of subsurface negative preformed nitrate anomalies in the subtropical North Pacific and North Atlantic

2018 ◽  
Vol 15 (21) ◽  
pp. 6461-6480 ◽  
Author(s):  
Robert T. Letscher ◽  
Tracy A. Villareal
Keyword(s):  
Time Series ◽  
Organic Matter ◽  
Water Column ◽  
North Atlantic ◽  
North Pacific ◽  
Nitrate Uptake ◽  
Inorganic Carbon ◽  
Dissolved Inorganic Carbon ◽  
Euphotic Zone ◽  
The North

Abstract. Summertime mixed-layer drawdown of dissolved inorganic carbon in the absence of measurable nutrients in the ocean's subtropical gyres and non-Redfieldian oxygen : nitrate relationships in the underlying subsurface waters are two biogeochemical phenomena that have thus far eluded complete description. Many processes are thought to contribute to one or both, including lateral nutrient transport, carbon overconsumption or non-Redfield C:N:P organic matter cycling, heterotrophic nutrient uptake, and the actions of vertically migrating phytoplankton. To obtain insight into the likely magnitude of potential contributing mechanisms that can remove nitrate from the nutricline while supporting dissolved inorganic carbon (DIC) drawdown tens of meters higher in the water column, we investigated the seasonal formation rates for negative preformed nitrate (preNO3) anomalies (oxygen consumption without stoichiometric nitrate release) in the subsurface and positive preformed nitrate anomalies (oxygen production without stoichiometric nitrate drawdown) in the euphotic zone at the subtropical ocean time series stations ALOHA (A Long-Term Oligotrophic Habitat Assessment) in the North Pacific and BATS (Bermuda Atlantic Time-series Study) in the North Atlantic. Non-Redfield -O2:N stoichiometry for dissolved organic matter (DOM) remineralization accounts for up to ∼15 mmol N m−2 yr−1 of negative preNO3 anomaly formation at both stations. We present a new formulation for calculating preNO3 (residual preNO3) that includes components resulting from non-Redfield DOM cycling. Residual negative preNO3 anomalies in excess of that which can be accounted for by non-Redfield DOM cycling are found to accumulate at a rate of ∼32–46 mmol N m−2 yr−1 at Station ALOHA and ∼46–87 mmol N m−2 yr−1 at the BATS station. These negative anomaly formation rates are in approximate balance with residual positive preNO3 anomaly formation rates from the euphotic zone located immediately above the nutricline in the water column. We evaluate three mechanisms to explain these anomalies, calculating that transparent exopolymer particle (TEP) cycling and heterotrophic nitrate uptake can contribute to the formation of both residual preNO3 anomalies. However, a significant fraction, estimated at ∼50 %–95 %, is unexplained by the sum of these processes. Vertically migrating phytoplankton possess the necessary distribution, nutrient acquisition strategy, and biogeochemical signature to simultaneously remove nitrate at depth and transport it above the nutricline. Reported transport rates by known migrators equal or exceed the residual preNO3 anomaly formation rates and potentially explain both the negative and positive residual preNO3 anomalies as well as the mixed-layer DIC drawdown at the stations ALOHA and BATS within the limits of scarce detailed abundance profiles. However, the three processes examined are not independent and mutually exclusive. The model Rhizosolenia mat system (and perhaps other migrators) produces TEPs, suggesting that migration could provide accelerated vertical transport of TEPs and provide labile carbon for heterotrophic nitrate uptake. These results based on geochemical distributions suggest that, in the absence of additional mechanisms and rates, phytoplankton vertical migrators, although rare and easily overlooked, play a larger role in subtropical ocean nutrient cycling and the biological pump than generally recognized.

A detrital zircon test of large-scale terrane displacement along the Arctic margin of North America

Geology ◽  
2021 ◽  
Author(s):  
Timothy M. Gibson ◽  
Karol Faehnrich ◽  
James F. Busch ◽  
William C. McClelland ◽  
Mark D. Schmitz ◽  
...  
Keyword(s):  
North America ◽  
Detrital Zircon ◽  
Large Scale ◽  
Small Sample ◽  
The Arctic ◽  
North Slope ◽  
The North ◽  
Arctic Alaska ◽  
Laurentian Margin ◽  
Small Sample Sizes

Detrital zircon U-Pb geochronology is one of the most common methods used to constrain the provenance of ancient sedimentary systems. Yet, its efficacy for precisely constraining paleogeographic reconstructions is often complicated by geological, analytical, and statistical uncertainties. To test the utility of this technique for reconstructing complex, margin-parallel terrane displacements, we compiled new and previously published U-Pb detrital zircon data (n = 7924; 70 samples) from Neoproterozoic–Cambrian marine sandstone-bearing units across the Porcupine shear zone of northern Yukon and Alaska, which separates the North Slope subterrane of Arctic Alaska from northwestern Laurentia (Yukon block). Contrasting tectonic models for the North Slope subterrane indicate it originated either near its current position as an autochthonous continuation of the Yukon block or from a position adjacent to the northeastern Laurentian margin prior to &gt;1000 km of Paleozoic–Mesozoic translation. Our statistical results demonstrate that zircon U-Pb age distributions from the North Slope subterrane are consistently distinct from the Yukon block, thereby supporting a model of continent-scale strike-slip displacement along the Arctic margin of North America. Further examination of this dataset highlights important pitfalls associated with common methodological approaches using small sample sizes and reveals challenges in relying solely on detrital zircon age spectra for testing models of terranes displaced along the same continental margin from which they originated. Nevertheless, large-n detrital zircon datasets interpreted within a robust geologic framework can be effective for evaluating translation across complex tectonic boundaries.

Integrating Visual and Bayesian Statistical Analyses in Single Case Experimental Research to Evaluate the Effectiveness and Magnitude of a Comprehensive Behavioral Intervention

2018 ◽  
Author(s):  
Prathiba Natesan ◽  
Smita Mehta
Keyword(s):  
Behavioral Intervention ◽  
Effect Size ◽  
Rate Ratio ◽  
Visual Analysis ◽  
Single Case ◽  
Small Sample ◽  
Statistical Analyses ◽  
Data Types ◽  
Ratio Effect ◽  
Small Sample Sizes

Single case experimental designs (SCEDs) have become an indispensable methodology where randomized control trials may be impossible or even inappropriate. However, the nature of SCED data presents challenges for both visual and statistical analyses. Small sample sizes, autocorrelations, data types, and design types render many parametric statistical analyses and maximum likelihood approaches ineffective. The presence of autocorrelation decreases interrater reliability in visual analysis. The purpose of the present study is to demonstrate a newly developed model called the Bayesian unknown change-point (BUCP) model which overcomes all the above-mentioned data analytic challenges. This is the first study to formulate and demonstrate rate ratio effect size for autocorrelated data, which has remained an open question in SCED research until now. This expository study also compares and contrasts the results from BUCP model with visual analysis, and rate ratio effect size with nonoverlap of all pairs (NAP) effect size. Data from a comprehensive behavioral intervention are used for the demonstration.

No Evidence that Experiencing Physical Warmth Promotes Interpersonal Warmth: Two Failures to Replicate Williams and Bargh (2008)

2018 ◽  
Author(s):  
Christopher Chabris ◽  
Patrick Ryan Heck ◽  
Jaclyn Mandart ◽  
Daniel Jacob Benjamin ◽  
Daniel J. Simons
Keyword(s):  
Null Hypothesis ◽  
Small Sample ◽  
Sample Sizes ◽  
Double Blind ◽  
Bayesian Analyses ◽  
Physical Warmth ◽  
Small Sample Sizes ◽  
Interpersonal Warmth

Williams and Bargh (2008) reported that holding a hot cup of coffee caused participants to judge a person’s personality as warmer, and that holding a therapeutic heat pad caused participants to choose rewards for other people rather than for themselves. These experiments featured large effects (r = .28 and .31), small sample sizes (41 and 53 participants), and barely statistically significant results. We attempted to replicate both experiments in field settings with more than triple the sample sizes (128 and 177) and double-blind procedures, but found near-zero effects (r = –.03 and .02). In both cases, Bayesian analyses suggest there is substantially more evidence for the null hypothesis of no effect than for the original physical warmth priming hypothesis.

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