11,875 research outputs found
Information Gap Activities: A Standards-Based Strategy for Promoting Oral Proficiency in a Thematic Context
This article demonstrates how the sustained use of standards-driven information gap activities (IGAs) supports and enhances the development of speaking skills. In the first section, we define the IGA. We then discuss recent research showing how IGAs promote focused student-student interactions. In the third section we provide a blueprint for implementing the IGA in a standards-based thematic context. We conclude with content-based models from a thematic unit on Argentina that are appropriate for both secondary and post-secondary classrooms
Preparing Tomorrow’s World Language Teacher Today: The Case for Seamless Induction
This essay is a call to action. It offers a comprehensive overview of the challenges facing world language (WL) teacher educators and their employers, the K-12 schools, during the teacher induction period. We propose a new paradigm for WL teacher education based on national accreditation standards, best-practice pedagogy, insights from the professional literature on methods education, and the enhanced role of the methods instructor/supervisor. In order to become successful in the classroom, the pre-service educator undergoes a seamless period of induction that is student-centered and college/university-supported beyond the classroom arena
Sugar additives for MALDI matrices improve signal allowing the smallest nucleotide change (A:T) in a DNA sequence to be resolved
Sample preparation for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) of DNA is critical for obtaining high quality mass spectra. Sample impurity, solvent content, substrate surface and environmental conditions (temperature and humidity) all affect the rate of matrix–analyte co-crystallization. As a result, laser fluence threshold for desorption/ionization varies from spot to spot. When using 3-hydroxypicolinic acid (3-HPA) as the matrix, laser fluence higher than the threshold value reduces mass resolution in time-of-flight (TOF) MS as the excess energy transferred to DNA causes metastable decay. This can be overcome by either searching for ‘hot’ spots or adjusting the laser fluence. However, both solutions may require a significant amount of operator manipulation and are not ideal for automatic measurements. We have added various sugars for crystallization with the matrix to minimize the transfer of excess laser energy to DNA molecules. Fructose and fucose were found to be the most effective matrix additives. Using these additives, mass resolution for DNA molecules does not show noticeable deterioration as laser energy increases. Improved sample preparation is important for the detection of single nucleotide polymorphisms (SNPs) using primer extension with a single nucleotide. During automatic data acquisition it is difficult to routinely detect heterozygous A/T mutations, which requires resolving a mass difference of 9 Da, unless a sugar is added during crystallization
Biological Consequences of Tightly Bent DNA: The Other Life of a Macromolecular Celebrity
The mechanical properties of DNA play a critical role in many biological
functions. For example, DNA packing in viruses involves confining the viral
genome in a volume (the viral capsid) with dimensions that are comparable to
the DNA persistence length. Similarly, eukaryotic DNA is packed in DNA-protein
complexes (nucleosomes) in which DNA is tightly bent around protein spools. DNA
is also tightly bent by many proteins that regulate transcription, resulting in
a variation in gene expression that is amenable to quantitative analysis. In
these cases, DNA loops are formed with lengths that are comparable to or
smaller than the DNA persistence length. The aim of this review is to describe
the physical forces associated with tightly bent DNA in all of these settings
and to explore the biological consequences of such bending, as increasingly
accessible by single-molecule techniques.Comment: 24 pages, 9 figure
Probing the Deep End of the Milky Way with New Oscillating Kepler Giants
The Kepler mission has been a success in both exoplanet search and stellar
physics studies. Red giants have actually been quite a highlight in the Kepler
scene. The Kepler long and almost continuous four-year observations allowed us
to detect oscillations in more than 15,000 red giants targeted by the mission.
However by looking at the power spectra of 45,000 stars classified as dwarfs
according to the Q1-16 Kepler star properties catalog, we detected red-giant
like oscillations in 850 stars. Even though this is a small addition to the
known red-giant sample, these misclassified stars represent a goldmine for
galactic archeology studies. Indeed they happen to be fainter (down to Kp~16)
and more distant (d>10kpc) than the known red giants, opening the possibility
to probe unknown regions of our Galaxy. The faintness of these red giants with
detected oscillations is very promising for detecting acoustic modes in red
giants observed with K2 and TESS. In this talk, I will present this new sample
of red giants with their revised stellar parameters derived from
asteroseismology. Then I will discuss about the distribution of their masses,
distances, and evolutionary states compared to the previously known sample of
red giants.Comment: 5 pages, 4 figures, Proceedings of the KASC9-TASC2 meetin
Dynamical Evolution of Globular Cluster Systems formed in Galaxy Mergers: Deep HST/ACS Imaging of Old and Intermediate-Age Globular Clusters in NGC 3610
(ABRIDGED) The ACS camera on board the Hubble Space Telescope has been used
to obtain deep images of the giant elliptical galaxy NGC 3610, a
well-established dissipative galaxy merger remnant. These observations
supersede previous WFPC2 images which revealed the presence of a population of
metal-rich globular clusters (GCs) of intermediate age (~1.5-4 Gyr). We detect
a total of 580 GC candidates, 46% more than from the previous WFPC2 images. The
new photometry strengthens the significance of the previously found bimodality
of the color distribution of GCs. Peak colors in V-I are 0.93 +/-0.01 and 1.09
+/- 0.01 for the blue and red subpopulations, respectively. The luminosity
function (LF) of the inner 50% of the metal-rich (`red') population of GCs
differs markedly from that of the outer 50%. In particular, the LF of the inner
50% of the red GCs shows a flattening consistent with a turnover that is about
1.0 mag fainter than the turnover of the blue GC LF. This is consistent with
predictions of recent models of GC disruption for the age range mentioned above
and for metallicities that are consistent with the peak color of the red GCs as
predicted by population synthesis models. We determine the specific frequency
of GCs in NGC 3610 and find a present-day value of S_N = 1.4 +/- 0.6. We
estimate that this value will increase to S_N = 3.8 +/- 1.7 at an age of 10
Gyr, which is consistent with typical S_N values for `normal' ellipticals. Our
findings constitute further evidence in support of the notion that metal-rich
GC populations formed during major mergers involving gas-rich galaxies can
evolve dynamically (through disruption processes) into the red, metal-rich GC
populations that are ubiquitous in `normal' giant ellipticals.Comment: 15 pages, 14 figures, 4 tables. Accepted for publication in The
Astronomical Journal. Figure 6 somewhat degraded to adhere to astro-ph rule
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