590 research outputs found
Think-aloud interviews: A tool for exploring student statistical reasoning
Research has shown that introductory statistics students hold many
misconceptions, and that many of these are also present among practicing
scientists. But statistics is becoming important to many new fields, and
understanding how students learn statistics is more important than ever, if it
is to be effectively taught. We describe an education research method intended
to reveal how students think and to provide practical ways of measuring their
understanding: a combination of think-aloud interviews and concept inventories.
Think-aloud interviews give unprecedented insight into student thinking, while
concept inventories can be administered to entire classes to measure learning.
We demonstrate the method through insights gained from 42 think-aloud
interviews with introductory students, plus large-scale concept inventory data
from over 50 questions given as pre- and post-tests to hundreds of introductory
statistics students at two institutions. Think-aloud interviews revealed
previously under-reported misconceptions about sampling distributions and
causation, while helping us refine conceptual questions to measure their
prevalence at large scale. These insights, and the final questions, may help
educators develop improved lessons, while suggesting directions for future
statistics education research and providing practical tools for researchers to
improve our understanding of student learning.Comment: 23 pages, 4 tables, 3 figures; supplemental data available online at
https://doi.org/10.1184/R1/1005844
External sovereign debt restructurings: Delay and replay
Today, more than half of low-income countries eligible for relief under the Debt Service Suspension Initiative (DSSI) are either in debt distress or at high risk. Several emerging markets have either recently restructured (Argentina and Ecuador) or remain in default (Lebanon, Surinam, and Venezuela). In this context, we review some of the features of external sovereign debt restructurings. We show that default spells are lengthy and that the road to debt-crisis resolution is often littered with serial restructuring agreements
Modeling the Ultrasonic Softening Effect for Robust Copper Wire Bonding
Unger A, Sextro W, Althoff S, et al. Modeling the Ultrasonic Softening Effect for Robust Copper Wire Bonding. In: 8th International Conference on Integrated Power Electronics Systems, Proceedings, February, 25-27, 2014 Nuremberg/Germany. ETG-Fachbericht. Vol 141. VDE-Verlag; 2014.In power electronics, ultrasonic wire bonding is
used to connect the electrical terminals of power modules.
To implement a self-optimization technique for ultrasonic wire
bonding machines, a model of the process is essential. This
model needs to include the so called ultrasonic softening effect.
It is a key effect within the wire bonding process primarily
enabling the robust interconnection between the wire and a
substrate. However, the physical modeling of the ultrasonic
softening effect is notoriously difficult because of its highly
non-linear character and the absence of a proper measurement
method. In a first step, this paper validates the importance of
modeling the ultrasonic softening by showing its impact on the
wire deformation characteristic experimentally. In a second step,
the paper presents a data-driven model of the ultrasonic softening
effect which is constructed from data using machine learning
techniques. A typical caveat of data-driven modeling is the need
for training data that cover the considered domain of process
parameters in order to achieve accurate generalization of the
trained model to new process configurations. In practice, however,
the space of process parameters can only be sampled sparsely.
In this paper, a novel technique is applied which enables the
integration of prior knowledge about the process into the datadriven
modeling process. It turns out that this approach results in
accurate generalization of the data-driven model to novel process
parameters from sparse data
The Political Color of Fiscal Responsibility
We propose a dynamic general equilibrium model that yields testable implications about the fiscal policy run by governments of different political color. Successive generations of voters choose taxation, expenditure, and government debt through repeated elections. Voters are heterogeneous by age and by the intensity of their preferences for public good provision. The political equilibrium switches stochastically between left- (pro-public goods) and right-leaning (pro-private consumption) governments. A shift to the left (right) is associated with a fall (increase) in government debt, an increase (fall) in taxation, and an increase (fall) in government expenditures. However, left-leaning governments engage in more debt accumulation during recessions. These predictions are shown to be consistent with the time-series evidence for the United States in the postwar period, and also with the evidence for a panel of OECD countries
Identification of pediatric septic shock subclasses based on genome-wide expression profiling
<p>Abstract</p> <p>Background</p> <p>Septic shock is a heterogeneous syndrome within which probably exist several biological subclasses. Discovery and identification of septic shock subclasses could provide the foundation for the design of more specifically targeted therapies. Herein we tested the hypothesis that pediatric septic shock subclasses can be discovered through genome-wide expression profiling.</p> <p>Methods</p> <p>Genome-wide expression profiling was conducted using whole blood-derived RNA from 98 children with septic shock, followed by a series of bioinformatic approaches targeted at subclass discovery and characterization.</p> <p>Results</p> <p>Three putative subclasses (subclasses A, B, and C) were initially identified based on an empiric, discovery-oriented expression filter and unsupervised hierarchical clustering. Statistical comparison of the three putative subclasses (analysis of variance, Bonferonni correction, <it>P </it>< 0.05) identified 6,934 differentially regulated genes. K-means clustering of these 6,934 genes generated 10 coordinately regulated gene clusters corresponding to multiple signaling and metabolic pathways, all of which were differentially regulated across the three subclasses. Leave one out cross-validation procedures indentified 100 genes having the strongest predictive values for subclass identification. Forty-four of these 100 genes corresponded to signaling pathways relevant to the adaptive immune system and glucocorticoid receptor signaling, the majority of which were repressed in subclass A patients. Subclass A patients were also characterized by repression of genes corresponding to zinc-related biology. Phenotypic analyses revealed that subclass A patients were younger, had a higher illness severity, and a higher mortality rate than patients in subclasses B and C.</p> <p>Conclusion</p> <p>Genome-wide expression profiling can identify pediatric septic shock subclasses having clinically relevant phenotypes.</p
Cystic Fibrosis isolates of Pseudomonas aeruginosa retain iron-regulated antimicrobial activity against Staphylococcus aureus through the action of multiple alkylquinolones
Cystic fibrosis (CF) is a hereditary disease that predisposes individuals to pulmonary dysfunction and chronic infections. Early infection of the CF lung with Staphylococcus aureus is common, while Pseudomonas aeruginosa becomes dominant as disease progresses. Emergence of P. aeruginosa likely depends on the action of multiple 2-alkyl-4-(1H)-quinolones (AQ) secreted by this organism. We recently showed that antimicrobial activity against S. aureus is enhanced by iron depletion and is dependent upon multiple AQ metabolites. Two of these AQs, the Pseudomonas quinolone signal [PQS; 2-heptyl-3-hydroxy-4(1H)-quinolone] and 2-heptyl-4-hydroxyquinoline (HHQ), are quorum sensing molecules that activate the expression of multiple microbicidal factors. Here we show for the first time that HHQ also exhibits innate antimicrobial activity against S. aureus. We further show that iron depletion potentiates the antistaphylococcal activity of HHQ, as well as 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO), another AQ that functions as a cytochrome B inhibitor. Notably, we found that deletion of the genes for the terminal biosynthetic steps for either PQS or HQNO results in overproduction of the HHQ intermediate, likely maintaining the ability of these mutants to mediate antimicrobial activity. Compensatory increases in HHQ were also observed in PQS-deficient CF isolates, which also retained the ability to mediate iron-regulated antimicrobial activity against S. aureus. These studies demonstrate that iron-regulated antimicrobial activity of P. aeruginosa against S. aureus is due to the cumulative effects of multiple AQ metabolites, both the production and activity of which are modulated by environmental iron levels
A “cell-friendly” window for the interaction of cells with hyaluronic acid/poly-L-lysine multilayers
Polyelectrolyte multilayers assembled from hyaluronic acid (HA) and poly-L-lysine (PLL) are most widely studied showing excellent reservoir characteristics to host molecules of diverse nature; however, thick (HA/PLL)n films were often found cell-repellent. By a systematic study of the adhesion and proliferation of various cells as a function of bilayer number ‘n’ a correlation with the mechanical and chemical properties of films is developed. The following cell lines have been studied: mouse 3T3 and L929 fibroblasts, human foreskin primary fibroblasts VH-Fib, human embryonic kidney HEK-293, human bone cell line U-2-OS, Chinese hamster ovary CHO-K and mouse embryonic stem cells. All cells adhere and spread well in a narrow ‘cell-friendly’ window, identified in the range of n=12-15. At n15, the film is cell-repellent for all cell lines. Cellular adhesion correlates with the mechanical properties of the films showing that softer films at higher ‘n’ number exhibiting a significant decrease of the Young’s modulus below 100 kPa are weakly adherent to cells. This trend cannot be reversed even by coating a strong cell-adhesive protein fibronectin onto the film. This indicates that mechanical cues plays a major role for cell behaviour, also in respect to biochemical ones
The politics and aesthetics of commemoration: national days in southern Africa
The contributions to the special section in this issue study recent independence celebrations and other national days in South
Africa, Namibia, Zimbabwe, Madagascar and the Democratic Republic of Congo. They explore the role of national days in
state-making and nation-building, and examine the performativity of nationalism and the role of performances in national
festivities. Placing the case studies in a broader, comparative perspective, the introduction first discusses the role of the state in
national celebrations, highlighting three themes: firstly, the political power-play and contested politics of memory involved in
the creation of a country’s festive calendar; secondly, the relationship between state control of national days and civic or
popular participation or contestation; and thirdly, the complex relationship between regional and ethnic loyalties and national
identifications. It then turns to the role of performance and aesthetics in the making of nations in general, and in national
celebrations in particular. Finally, we look at the different formats and meanings of national days in the region and address the
question whether there is anything specific about national days in southern Africa as compared to other parts of the continent
or national celebrations world-wide.Web of Scienc
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