3,271 research outputs found
Interpreting the Hydrogen IR Lines - Impact of Improved Electron Collision Data
We evaluate the effect of variations in the electron-impact excitation cross
sections on the non-LTE line formation for hydrogen in early-type stars. While
the Balmer lines are basically unaffected by the choice of atomic data, the
Brackett and Pfund series members allow us to discriminate between the
different models. Non-LTE calculations based on the widely-used approximations
of Mihalas, Heasley & Auer and of Johnson fail to simultaneously reproduce the
observed optical and IR spectra over the entire parameter range. Instead, we
recommend a reference model using data from ab-initio calculations up to
principal quantum number n<=7 for quantitative work. This model is of general
interest due to the ubiquity of the hydrogen spectrum.Comment: 6 pages, 6 figure
Ferroelectric Materials for Solar Energy Conversion: Photoferroics Revisited
The application of ferroelectric materials (i.e. solids that exhibit
spontaneous electric polarisation) in solar cells has a long and controversial
history. This includes the first observations of the anomalous photovoltaic
effect (APE) and the bulk photovoltaic effect (BPE). The recent successful
application of inorganic and hybrid perovskite structured materials (e.g.
BiFeO3, CsSnI3, CH3NH3PbI3) in solar cells emphasises that polar semiconductors
can be used in conventional photovoltaic architectures. We review developments
in this field, with a particular emphasis on the materials known to display the
APE/BPE (e.g. ZnS, CdTe, SbSI), and the theoretical explanation. Critical
analysis is complemented with first-principles calculation of the underlying
electronic structure. In addition to discussing the implications of a
ferroelectric absorber layer, and the solid state theory of polarisation (Berry
phase analysis), design principles and opportunities for high-efficiency
ferroelectric photovoltaics are presented
Electronic chemical potentials of porous metal-organic frameworks
The binding energy of an electron in a material is a fundamental
characteristic, which determines a wealth of important chemical and physical
properties. For metal-organic frameworks this quantity is hitherto unknown. We
present a general approach for determining the vacuum level of porous
metal-organic frameworks and apply it to obtain the first ionisation energy for
six prototype materials including zeolitic, covalent and ionic frameworks. This
approach for valence band alignment can explain observations relating to the
electrochemical, optical and electrical properties of porous frameworks
Long Live the Dead Hand: A Case for Repeal of the Rule Against Perpetuities in Washington
The common law rule against perpetuities has had a storied career spanning several centuries and two legal systems. The rule developed to curb the concentration of wealth in the hands of a few, and to limit the control of property by those no longer alive to use it. Legendary for its complexity, the rule has undergone statutory reform in many states; some states have gone so fara s to repeal the rule outright. Washington has embraced two of the major reforms of the rule and is considering repeal. This Comment argues that the rule, even with reform, no longer serves the policies for which it was designed. The threats posed by dead hand control are no longer pressing, and extant legal mechanisms are adequate to deal with the threats that remain. Reform is too mild a response to the rule\u27s shortcomings. Washington, therefore, should repeal the rule
I Live in a Place That a River Runs Through: Localized Literacy, Currere and a Summer in an Ojibway Community
In this paper, I analyze a particular artifact from my lived curriculum – a short children’s book I wrote while running a literacy program in an Ojibway community. In doing this, I draw upon Ng-A-Fook’s (2011) (re)imagining of currere as specific experiential snapshots that open up into wider landscapes of meaning. After situating the book within my own lived experience, I unlock some of the meanings contained in it by analyzing it through three different theoretical lenses. I first examine the book in relation to research on place-based literacy (e.g. Kulnieks, Longboat, & Young, 2010), and suggest the value of such a localized approach to literacy education. Secondly, in relation to the scholarship on settler colonialism (e.g. Tuck & Gaztambide-Fernández, 2013), I question whether my choice as an outsider to write a work of “literature” incorporating aspects of local intergenerational knowledges should be seen an act of appropriation. Thirdly, I draw on literature arguing for the development of ethical intercultural meeting places (e.g. Haig-Brown, 2008) in order to suggest that this artifact is best understood as a record of my gradual development as an educator and a researcher. I suggest that currere is not just a way for teachers to become “amateur intellectuals” (Kanu & Glor, 2006), but also a way for researchers like such as myself to become “amateur practitioners,” by learning to situate our experience within the skilled practices of a curriculum of place (Chambers, 2008)
Non-LTE line-formation for CNO
Accurate atomic data have become available in the recent past due to the
demands of astrophysics and fusion research. We report on the impact of such
data on non-LTE line-formation calculations for CNO in early-type stars.
Considerable improvement is achieved by the derivation of consistent results
from practically all available spectroscopic indicators, regardless of
ionization stage or spin system, and the uncertainties in the analyses are
drastically reduced. Moreover, systematic trends are revealed, e.g. an increase
of the NI abundances from previous studies of BA-type supergiants by a factor
of two is indicated. The present work promises stringent observational
constraints on chemical mixing in the course of massive star evolution. First
results on BA-type supergiants in the Galaxy and the Magellanic Clouds are
discussed.Comment: 6 pages, 2 figures; to be published in "CNO in the Universe", ASP
Conf. Series, eds. C. Charbonnel, D. Schaerer & G. Meyne
Getting into sheep an introductory guide to sheep management
Sheep husbandry can be an interesting and rewarding activity but before starting to work with or buy sheep ask yourself if you are prepared to spend the time and effort to care for them.
Sheep cannot be placed in a paddock and forgotten. The sheep, along with their water, feed and fences must be inspected regularly. If you do not live on the farm, or visit it only infrequently, make sure there is a responsible person available who is willing to inspect and manage the sheep on your behalf.https://researchlibrary.agric.wa.gov.au/bulletins/1201/thumbnail.jp
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