487 research outputs found
A statistical study of variation in the catch of plankton nets
Staternent of the Problern.----In a previous communication, Winsor and Walford (1936) analyzed the results of repeated vertical hauls of different types of plankton nets, making use of data available in the literature. They concluded that the observed results could be accounted for reasonably well on the assumptions that (a) the organisms were randomly distributed in the medium and (b) that the volume of medium effectively sampled varied from haul to haul. From this result it follows that as the total catch is increased (as by increasing the net size) the reliability of a population estimate is ultimately limited by variation in volume sampled; and that where such conditions hold, it is useless to attempt greater accuracy by increasing either the total catch or the fraction counted much beyond the point where 100 organisms of the kind in question are counted
Linking the 8.2 ka Event and its Freshwater Forcing in the Labrador Sea
The 8.2 ka event was the last deglacial abrupt climate event. A reduction in the Atlantic meridional overturning circulation (AMOC) attributed to the drainage of glacial Lake Agassiz may have caused the event, but the freshwater signature of Lake Agassiz discharge has yet to be identified in (delta)18O of foraminiferal calcite records from the Labrador Sea, calling into question the connection between freshwater discharge to the North Atlantic and AMOC strength. Using Mg/Ca-paleothermometry, we demonstrate that approx. 3 C of near-surface ocean cooling masked an 1.0 % decrease in western Labrador Sea (delta)18O of seawater concurrent with Lake Agassiz drainage. Comparison with North Atlantic (delta)18O of seawater records shows that the freshwater discharge was transported to regions of deep-water formation where it could perturb AMOC and force the 8.2 ka event
Evidence for the Gompertz Curve in the Income Distribution of Brazil 1978-2005
This work presents an empirical study of the evolution of the personal income
distribution in Brazil. Yearly samples available from 1978 to 2005 were studied
and evidence was found that the complementary cumulative distribution of
personal income for 99% of the economically less favorable population is well
represented by a Gompertz curve of the form , where
is the normalized individual income. The complementary cumulative
distribution of the remaining 1% richest part of the population is well
represented by a Pareto power law distribution . This
result means that similarly to other countries, Brazil's income distribution is
characterized by a well defined two class system. The parameters , ,
, were determined by a mixture of boundary conditions,
normalization and fitting methods for every year in the time span of this
study. Since the Gompertz curve is characteristic of growth models, its
presence here suggests that these patterns in income distribution could be a
consequence of the growth dynamics of the underlying economic system. In
addition, we found out that the percentage share of both the Gompertzian and
Paretian components relative to the total income shows an approximate cycling
pattern with periods of about 4 years and whose maximum and minimum peaks in
each component alternate at about every 2 years. This finding suggests that the
growth dynamics of Brazil's economic system might possibly follow a
Goodwin-type class model dynamics based on the application of the
Lotka-Volterra equation to economic growth and cycle.Comment: 22 pages, 15 figures, 4 tables. LaTeX. Accepted for publication in
"The European Physical Journal B
Pressure Induced Topological Phase Transitions in Membranes
Some highly unusual features of a lipid-water liquid crystal are revealed by
high pressure x-ray diffraction, light scattering and dilatometric studies of
the lamellar (bilayer ) to nonlamellar inverse hexagonal ()
phase transition. (i) The size of the unit cell of the phase increases
with increasing pressure. (ii) The transition volume, ,
decreases and appears to vanish as the pressure is increased. (iii) The
intensity of scattered light increases as decreases. Data are
presented which suggest that this increase is due to the formation of an
intermediate cubic phase, as predicted by recent theoretical suggestions of the
underlying universal phase sequence.Comment: 12 pages, typed using REVTEX 2.
Expanding Efficiency: Women\u27s Communication in Engineering
As engineering fields strive to be more inclusive of women, focusing on perceptions of women\u27s work is vital to understanding how women can succeed and the limitations they may face. One area in need of more attention is the connection between communication and women\u27s experiences in engineering. This article examines the gendered nature of writing labor in engineering, focusing on case studies of three women who were able to use writing effectively, yet how communication emerged as a gendered form of labor subject to gendered perceptions. While these women\u27s communication skills led to professional success, their association with writing echoes a historical division, where writing is viewed as less valuable than technical knowledge. This division has the potential to disadvantage women who are asked to take on more writing-related tasks. In addition, their writing and communication are subject to gendered perceptions of being ‘chatty’ or blunt rather than effective or efficient. Articulating these perceptions and attitudes can lead to a breakdown of the binary between writing and technical labor as well as appropriately valuing the contributions women make in engineering through writing
Comparative genomics of isolates of a pseudomonas aeruginosa epidemic strain associated with chronic lung infections of cystic fibrosis patients
Pseudomonas aeruginosa is the main cause of fatal chronic lung infections among individuals suffering from cystic fibrosis (CF). During the past 15 years, particularly aggressive strains transmitted among CF patients have been identified, initially in Europe and more recently in Canada. The aim of this study was to generate high-quality genome sequences for 7 isolates of the Liverpool epidemic strain (LES) from the United Kingdom and Canada representing different virulence characteristics in order to: (1) associate comparative genomics results with virulence factor variability and (2) identify genomic and/or phenotypic divergence between the two geographical locations. We performed phenotypic characterization of pyoverdine, pyocyanin, motility, biofilm formation, and proteolytic activity. We also assessed the degree of virulence using the Dictyostelium discoideum amoeba model. Comparative genomics analysis revealed at least one large deletion (40-50 kb) in 6 out of the 7 isolates compared to the reference genome of LESB58. These deletions correspond to prophages, which are known to increase the competitiveness of LESB58 in chronic lung infection. We also identified 308 non-synonymous polymorphisms, of which 28 were associated with virulence determinants and 52 with regulatory proteins. At the phenotypic level, isolates showed extensive variability in production of pyocyanin, pyoverdine, proteases and biofilm as well as in swimming motility, while being predominantly avirulent in the amoeba model. Isolates from the two continents were phylogenetically and phenotypically undistinguishable. Most regulatory mutations were isolate-specific and 29% of them were predicted to have high functional impact. Therefore, polymorphism in regulatory genes is likely to be an important basis for phenotypic diversity among LES isolates, which in turn might contribute to this strain's adaptability to varying conditions in the CF lung
Magnetic confinement of an electric arc in transverse supersonic flow
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77344/1/AIAA-2803-657.pd
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Linking the 8.2 ka event and its freshwater forcing in the Labrador Sea
The 8.2 ka event was the last deglacial abrupt climate event. A reduction in the Atlantic meridional overturning circulation (AMOC) attributed to the drainage of glacial Lake Agassiz may have caused the event, but the freshwater signature of Lake Agassiz discharge has yet to be identified in δ¹⁸O of foraminiferal calcite records from the Labrador Sea, calling into question the connection between freshwater discharge to the North Atlantic and AMOC strength. Using Mg/Ca-paleothermometry, we demonstrate that ∼3°C of near-surface ocean cooling masked an ∼1.0‰ decrease in western Labrador Sea δ¹⁸O of seawater concurrent with Lake Agassiz drainage. Comparison with North Atlantic δ¹⁸O of seawater records shows that the freshwater discharge was transported to regions of deep-water formation where it could perturb AMOC and force the 8.2 ka event
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