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Teacher research as a response to Miss, do we really have to pass this class? : examining discourses in the middle school students\u27 foreign language classroom.
It seems a paradox that the United States, a country with a highly diverse population and a long history of immigration, has one of the poorest records of sustained public foreign language programs when compared to similar post industrial countries. In an educational system such as the one in United States that is not centralized, foreign language instruction appears not to be a real, tangible necessity. In this situation are engulfed many school districts that are left with state and/or national guidelines and an ever-changing budget, to decide who should learn what languages, if any. By framing and understanding the foreign language education in this context, this ethnographic study examines through a post-structuralist perspective, a current program in the United States and looks specifically at how issues of motivation and power get constructed by students in the foreign language classroom of an urban middle school setting. This study also examines how language policies enacted through class instruction impact student endorsement of foreign language education during the formative years in U.S. public schools that may influence learning, and may generate resistance, or lack of motivation to learn a foreign language. Critical discourse analysis is employed in this study as a tool to: (1) review and analyze specific recent legislation that is interpreted and enacted in the foreign language program of a local school system, (2) examine data collected through interviews with students and administrators, and (3) understand classroom interactions within the local political context of a school system. In examining the social, textual and discursive levels of these policies, it is possible to challenge how traditional education defines the roles of teachers and students and to envision new relations of power that could condition the existence of new learners\u27 identities and new possibilities for teachers. This study will contribute towards the understanding of classroom practices in foreign language programs as they influence and are influenced by language planning and policy decisions, and so point to areas where change can be made. In terms of stating the practical implications for the foreign language field, the concept of student endorsement, as it is employed in this study, is examined for its potential as a viable replacement for the traditional notion of student motivation. Understanding endorsement issues in relation to the current language policies on learning situates learning not as an individual psychological factor but rather as a socially shaped response that can be changed. Furthermore, teachers\u27 and administrators\u27 understanding of endorsement could challenge current policies and practices that contribute to the devaluing and reduction of benefits of foreign language instruction
These are not the k-mers you are looking for: efficient online k-mer counting using a probabilistic data structure
K-mer abundance analysis is widely used for many purposes in nucleotide
sequence analysis, including data preprocessing for de novo assembly, repeat
detection, and sequencing coverage estimation. We present the khmer software
package for fast and memory efficient online counting of k-mers in sequencing
data sets. Unlike previous methods based on data structures such as hash
tables, suffix arrays, and trie structures, khmer relies entirely on a simple
probabilistic data structure, a Count-Min Sketch. The Count-Min Sketch permits
online updating and retrieval of k-mer counts in memory which is necessary to
support online k-mer analysis algorithms. On sparse data sets this data
structure is considerably more memory efficient than any exact data structure.
In exchange, the use of a Count-Min Sketch introduces a systematic overcount
for k-mers; moreover, only the counts, and not the k-mers, are stored. Here we
analyze the speed, the memory usage, and the miscount rate of khmer for
generating k-mer frequency distributions and retrieving k-mer counts for
individual k-mers. We also compare the performance of khmer to several other
k-mer counting packages, including Tallymer, Jellyfish, BFCounter, DSK, KMC,
Turtle and KAnalyze. Finally, we examine the effectiveness of profiling
sequencing error, k-mer abundance trimming, and digital normalization of reads
in the context of high khmer false positive rates. khmer is implemented in C++
wrapped in a Python interface, offers a tested and robust API, and is freely
available under the BSD license at github.com/ged-lab/khmer
A Reference-Free Algorithm for Computational Normalization of Shotgun Sequencing Data
Deep shotgun sequencing and analysis of genomes, transcriptomes, amplified
single-cell genomes, and metagenomes has enabled investigation of a wide range
of organisms and ecosystems. However, sampling variation in short-read data
sets and high sequencing error rates of modern sequencers present many new
computational challenges in data interpretation. These challenges have led to
the development of new classes of mapping tools and {\em de novo} assemblers.
These algorithms are challenged by the continued improvement in sequencing
throughput. We here describe digital normalization, a single-pass computational
algorithm that systematizes coverage in shotgun sequencing data sets, thereby
decreasing sampling variation, discarding redundant data, and removing the
majority of errors. Digital normalization substantially reduces the size of
shotgun data sets and decreases the memory and time requirements for {\em de
novo} sequence assembly, all without significantly impacting content of the
generated contigs. We apply digital normalization to the assembly of microbial
genomic data, amplified single-cell genomic data, and transcriptomic data. Our
implementation is freely available for use and modification
Challenges and opportunities in understanding microbial communities with metagenome assembly (accompanied by IPython Notebook tutorial)
Metagenomic investigations hold great promise for informing the genetics, physiology, and ecology of environmental microorganisms. Current challenges for metagenomic analysis are related to our ability to connect the dots between sequencing reads, their population of origin, and their encoding functions. Assembly-based methods reduce dataset size by extending overlapping reads into larger contiguous sequences (contigs), providing contextual information for genetic sequences that does not rely on existing references. These methods, however, tend to be computationally intensive and are again challenged by sequencing errors as well as by genomic repeats While numerous tools have been developed based on these methodological concepts, they present confounding choices and training requirements to metagenomic investigators. To help with accessibility to assembly tools, this review also includes an IPython Notebook metagenomic assembly tutorial. This tutorial has instructions for execution any operating system using Amazon Elastic Cloud Compute and guides users through downloading, assembly, and mapping reads to contigs of a mock microbiome metagenome. Despite its challenges, metagenomic analysis has already revealed novel insights into many environments on Earth. As software, training, and data continue to emerge, metagenomic data access and its discoveries will to grow
Assembling large, complex environmental metagenomes
The large volumes of sequencing data required to sample complex environments
deeply pose new challenges to sequence analysis approaches. De novo metagenomic
assembly effectively reduces the total amount of data to be analyzed but
requires significant computational resources. We apply two pre-assembly
filtering approaches, digital normalization and partitioning, to make large
metagenome assemblies more comput\ ationaly tractable. Using a human gut mock
community dataset, we demonstrate that these methods result in assemblies
nearly identical to assemblies from unprocessed data. We then assemble two
large soil metagenomes from matched Iowa corn and native prairie soils. The
predicted functional content and phylogenetic origin of the assembled contigs
indicate significant taxonomic differences despite similar function. The
assembly strategies presented are generic and can be extended to any
metagenome; full source code is freely available under a BSD license.Comment: Includes supporting informatio
Avalanches and the Distribution of Reconnection Events in Magnetized Circumstellar Disks
Cosmic rays produced by young stellar objects can potentially alter the
ionization structure, heating budget, chemical composition, and accretion
activity in circumstellar disks. The inner edges of these disks are truncated
by strong magnetic fields, which can reconnect and produce flaring activity
that accelerates cosmic radiation. The resulting cosmic rays can provide a
source of ionization and produce spallation reactions that alter the
composition of planetesimals. This reconnection and particle acceleration are
analogous to the physical processes that produce flaring in and heating of
stellar coronae. Flaring events on the surface of the Sun exhibit a power-law
distribution of energy, reminiscent of those measured for Earthquakes and
avalanches. Numerical lattice-reconnection models are capable of reproducing
the observed power-law behavior of solar flares under the paradigm of
self-organized criticality. One interpretation of these experiments is that the
solar corona maintains a nonlinear attractor -- or ``critical'' -- state by
balancing energy input via braided magnetic fields and output via reconnection
events. Motivated by these results, we generalize the lattice-reconnection
formalism for applications in the truncation region of magnetized disks. Our
numerical experiments demonstrate that these nonlinear dynamical systems are
capable of both attaining and maintaining criticality in the presence of
Keplerian shear and other complications. The resulting power-law spectrum of
flare energies in the equilibrium attractor state is found to be nearly
universal in magnetized disks. This finding indicates that magnetic
reconnection and flaring in the inner regions of circumstellar disks occur in a
manner similar to activity on stellar surfaces
Probing the Catalytic Roles of Arg548 and Gln552 in the Carboxyl Transferase Domain of the \u3cem\u3eRhizobium etli\u3c/em\u3e Pyruvate Carboxylase by Site-directed Mutagenesis
The roles of Arg548 and Gln552 residues in the active site of the carboxyl transferase domain of Rhizobium etli pyruvate carboxylase were investigated using site-directed mutagenesis. Mutation of Arg548 to alanine or glutamine resulted in the destabilization of the quaternary structure of the enzyme, suggesting that this residue has a structural role. Mutations R548K, Q552N, and Q552A resulted in a loss of the ability to catalyze pyruvate carboxylation, biotin-dependent decarboxylation of oxaloacetate, and the exchange of protons between pyruvate and water. These mutants retained the ability to catalyze reactions that occur at the active site of the biotin carboxylase domain, i.e., bicarbonate-dependent ATP cleavage and ADP phosphorylation by carbamoyl phosphate. The effects of oxamate on the catalysis in the biotin carboxylase domain by the R548K and Q552N mutants were similar to those on the catalysis of reactions by the wild-type enzyme. However, the presence of oxamate had no effect on the reactions catalyzed by the Q552A mutant. We propose that Arg548 and Gln552 facilitate the binding of pyruvate and the subsequent transfer of protons between pyruvate and biotin in the partial reaction catalyzed in the active site of the carboxyl transferase domain of Rhizobium etli pyruvate carboxylase
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