The oldest, most metal-poor stars in the Galactic halo and satellite dwarf galaxies present an opportunity to explore the chemical and physical conditions of the earliest star-forming environments in ...the Universe. We review the fields of stellar archaeology and dwarf galaxy archaeology by examining the chemical abundance measurements of various elements in extremely metal-poor stars. Focus on the carbon-rich and carbon-normal halo star populations illustrates how these provide insight into the Population III star progenitors responsible for the first metal enrichment events. We extend the discussion to near-field cosmology, which is concerned with the formation of the first stars and galaxies, and how metal-poor stars can be used to constrain these processes. Complementary abundance measurements in high-redshift gas clouds further help establish the early chemical evolution of the Universe. The data appear consistent with the existence of two distinct channels of star formation at the earliest times.
We explore the nature of carbon-rich (C/Fe1D,LTE > +0.7), metal-poor (Fe/H1D,LTE < −2.0) stars in the light of post 1D,LTE literature analyses, which provide 3D-1D and NLTE-LTE corrections for iron, ...and 3D-1D corrections for carbon (from the CH G-band, the only indicator at lowest Fe/H). High-excitation C i lines are used to constrain 3D,NLTE corrections of G-band analyses. Corrections to the 1D,LTE compilations of Yoon et al. and Yong et al. yield 3D,LTE and 3D,NLTE Fe and C abundances. The number of CEMP-no stars in the Yoon et al. compilation (plus eight others) decreases from 130 (1D,LTE) to 68 (3D,LTE) and 35 (3D,NLTE). For stars with −4.5 < Fe/H < −3.0 in the compilation of Yong et al., the corresponding CEMP-no fractions change from 0.30 to 0.15 and 0.12, respectively. We present a toy model of the coalescence of pre-stellar clouds of the two populations that followed chemical enrichment by the first zero-heavy-element stars: the C-rich, hyper-metal-poor and the C-normal, very-metal-poor populations. The model provides a reasonable first-order explanation of the distribution of the 1D,LTE abundances of CEMP-no stars in the A(C) and C/Fe versus Fe/H planes, in the range −4.0 < Fe/H < −2.0. The Yoon et al. CEMP Group I contains a subset of 19 CEMP-no stars (14% of the group), four out of nine of which are binary, and which have large Sr/Ba1D,LTE values. The data support the conjectures of Hansen et al. and Arentsen et al. that these stars may have experienced enrichment from asymptotic giant branch stars and/or "spinstars."
Almost as soon as a viable metal-framed bike was invented, it was put to military use, offering a much cheaper, less fragile and less logistically demanding alternative to horse transport. Widely ...used in many armies from the late 19th century, through both world wars and beyond, the bicycle really is the forgotten war machine. John Norris traces traces the development of military cycling from first experiments, including early (often flawed) designs for armed and multi-passenger versions. He explains how any why bikes were used for rapid movement of infantry units as well as carrying messages and other tasks.First used in the Franco-Prussian War of 1870-71, then by both sides in the Boer War, they were widely adopted throughout Europe before the First World War. In the Second World War, the Japanese used over fifty thousand bicycles in the conquest of Malaya and the German army used over three million, relying on them increasingly as petrol shortages immobilized motor transport. The Allies famously made use of folding and air-dropped bikes in Operation Market Garden and in Normandy. After WW2 bikes were used extensively in Vietnam, particularly along the Ho Chi Minh trail and some European armies maintained specialist bicycle units throughout the Cold War and into the 21st century. Specialized military bikes, collapsible for use by parachutists, are still being made for Special Forces units. John Norris examines the whole history of pedal-powered warfare and illustrates it with an array of high-quality photographs.
Traditions of statistical significance testing in second language (L2) quantitative research are strongly entrenched in how researchers design studies, select analyses, and interpret results. ...However, statistical significance tests using p values are commonly misinterpreted by researchers, reviewers, readers, and others, leading to confusion regarding the actual findings of primary studies and critical challenges for the accumulation of meaningful knowledge about language learning research. This paper outlines the basic challenges of accurately calculating and interpreting statistical significance tests, explores common examples of incorrect interpretations in L2 research, and proposes strategies for resolving these problems.
We measure the C+N+O abundance sum in red giant stars in two Galactic globular clusters, NGC 1851 and NGC 6752. NGC 1851 has a split subgiant branch which could be due to different ages or C+N+O ...content while NGC 6752 is representative of the least complex globular clusters. For NGC 1851 and NGC 6752, we obtain average values of A(C+N+O) = 8.16 plus or minus 0.10 ( sigma = 0.34) and 7.62 plus or minus 0.02 ( sigma = 0.06), respectively. When taking into account the measurement errors, we find a constant C+N+O abundance sum in NGC 6752. The C+N+O abundance dispersion is only 0.06 dex, and such a result requires that the source of the light element abundance variations does not increase the C+N+O sum in this cluster. For NGC 1851, we confirm a large spread in C+N+O. In this cluster, the anomalous RGB has a higher C+N+O content than the canonical RGB by a factor of 4 ( similar to 0.6 dex). This result lends further support to the idea that the two subgiant branches in NGC 1851 are roughly coeval, but with different CNO abundances.
In this article, we examine current practices in the measurement of syntactic complexity to illustrate the need for more organic and sustainable practices in the measurement of complexity, accuracy, ...and fluency (CAF) in second language production. Through in-depth review of examples drawn from research on instructed second language acquisition, we identify and discuss challenges to the evidentiary logic that underlies current approaches. We also illuminate critical mismatches between the interpretations that researchers want to make and the complexity measures that they use to make them. Building from the case of complexity, we point to related concerns with impoverished operationalizations of multidimensional CAF constructs and the lack of attention to CAF as a dynamic and interrelated set of constantly changing subsystems. In conclusion, we offer suggestions for addressing these challenges, and we call for much closer articulation between theory and measurement as well as more central roles for multidimensionality and dynamicity in future CAF research.
Abstract
We present chemical abundance measurements for seven stars with metallicities ranging from Fe/H = −3.3 to Fe/H = −2.4 in the Tucana II ultra-faint dwarf galaxy (UFD), based on ...high-resolution spectra obtained with the MIKE spectrograph on the 6.5 m Magellan-Clay Telescope. For three stars, we present detailed chemical abundances for the first time. Of those, two stars are newly discovered members of Tucana II and were selected as probable members from deep narrowband photometry of the Tucana II UFD taken with the SkyMapper telescope. This result demonstrates the potential for photometrically identifying members of dwarf galaxy systems based on chemical composition. One new star was selected from the membership catalog of Walker et al. The other four stars in our sample have been reanalyzed, following additional observations. Overall, six stars have chemical abundances that are characteristic of the UFD stellar population. The seventh star shows chemical abundances that are discrepant from the other Tucana II members and an atypical, higher strontium abundance than what is expected for typical UFD stars. While unlikely, its strontium abundance raises the possibility that it may be a foreground metal-poor halo star with the same systemic velocity as Tucana II. If we were to exclude this star, Tucana II would satisfy the criteria to be a surviving first galaxy. Otherwise, this star implies that Tucana II has likely experienced somewhat extended chemical evolution.
Drugs that inhibit estrogen receptor alpha (ERα) or that block the production of estrogens remain frontline interventions in the treatment and management of breast cancer at all stages. However, ...resistance to endocrine therapies, especially in the setting of advanced disease, remains an impediment to durable clinical responses. Although the mechanisms underlying resistance to existing agents are complex, preclinical studies suggest that selective estrogen receptor downregulators (SERDs), molecules which eliminate ERα expression, may have particular utility in the treatment of breast cancers that have progressed on tamoxifen and/or aromatase inhibitors. The discovery and development of orally bioavailable SERDs provide the opportunity to evaluate the utility of eliminating ERα expression in advanced metastatic breast cancers.
Language Program Evaluation Norris, John M.
The Modern language journal (Boulder, Colo.),
Supplement 2016, Letnik:
100, Številka:
S1
Journal Article
Recenzirano
Language program evaluation is a pragmatic mode of inquiry that illuminates the complex nature of language-related interventions of various kinds, the factors that foster or constrain them, and the ...consequences that ensue. Program evaluation enables a variety of evidence-based decisions and actions, from designing programs and implementing practices to judging effectiveness and improving outcomes. Though often narrowly construed as an external accountability requirement only, evaluation may provide a heuristic for generating new knowledge; raising awareness; and transforming the educational, social, and economic circumstances of individuals and communities. In this article, I review the origins and interdisciplinary nature of program evaluation, and I trace its development within applied linguistics and language education in particular. I then consider the current contributions of language program evaluation, and I point to likely future trends. In particular, I highlight how changing global circumstances, technological affordances, and contexts and purposes for language learning and language use are both impacting the nature of evaluation and presenting challenges for which evaluation is uniquely suited to respond. I also emphasize the potential—versus as yet realized—contribution of program evaluation as a way of ameliorating gaps in current language research and practice, and I point to implications for training, dissemination, and integration of this mode of inquiry as an important part of the future intellectual core of applied linguistics.
The Helium Abundances of ω Centauri Norris, John E
Astrophysical journal/The Astrophysical journal,
09/2004, Letnik:
612, Številka:
1
Journal Article
PDF
