39,223 research outputs found
Recommended from our members
Tutor Handbooks: Heuristic Texts for Negotiating Difference in a Globalized World
I would like to begin this article by telling a true
story. When I was a graduate student earning my
doctoral degree, I worked in a writing center on a
midsized and predominantly white university campus.
Every week I attended and sometimes facilitated the
writing center’s tutor education workshop. At one of
these meetings, an undergraduate tutor from a Euro-
American background said that one of the things she
liked about working at the writing center was that if
she had a question about grammar during a
conference with a client, she could simply lean over to
the next table and ask another tutor for advice. In
response to this statement, an African-American tutor
said that she would never ask another tutor for
grammar help because she felt that doing so would
undermine her authority and lead clients to question
her competence in Standard American English. At this
point a bilingual Asian-American tutor said that clients
often doubted her ability to tutor based solely on her
appearance. For many of her American clients she was
too foreign, while for many of her international clients
she was not American enough. This discussion was a
revelation for many of the Euro-American tutors,
since it had never occurred to them that one’s physical
appearance could bring his or her linguistic
competence into question. All of the tutors learned a
great deal from this remarkable discussion, and the
theory and practice of the writing center shifted in
ways that more fully accounted for the experiences of
tutors from diverse backgrounds.
I tell this story for two reasons.University Writing Cente
Can Modern Nuclear Hamiltonians Tolerate a Bound Tetraneutron?
I show that it does not seem possible to change modern nuclear Hamiltonians
to bind a tetraneutron without destroying many other successful predictions of
those Hamiltonians. This means that, should a recent experimental claim of a
bound tetraneutron be confirmed, our understanding of nuclear forces will have
to be significantly changed. I also point out some errors in previous
theoretical studies of this problem.Comment: 4 pages, 4 figures Revision corrects a pronou
The scaling of secondary craters
Secondary craters are common features around fresh planetary-scale primary impact craters throughout most of the Solar System. They derive from the ejection phase of crater formation, thus secondary scaling relations provide constraints on parameters affecting ejection processes. Secondary crater fields typically begin at the edge of the continuous ejecta blankets (CEB) and extend out several crater radii. Secondaries tend to have rounded rims and bilateral symmetry about an axis through the primary crater's center. Prominent secondary chains can extend inward across the CEB close to the rim. A simple method for comparing secondary crater fields was employed: averaging the diameters and ranges from the center of the primary crater of the five largest craters in a secondary crater field. While not as much information is obtained about individual crater fields by this method as in more complete secondary field mapping, it facilitates rapid comparison of many secondary fields. Also, by quantifying a few specific aspects of the secondary crater field, this method can be used to construct scaling relations for secondary craters
Mechanical and thermal properties of planetologically important ices
Two squences of ice composition were proposed for the icy satellites: a dense nebula model and a solar nebula model. Careful modeling of the structure, composition, and thermal history of satellites composed of these various ices requires quantitative information on the density, compressibility, thermal expansion, heat capacity, and thermal conductivity. Equations of state were fitted to the density data of the molecular ices. The unusual thermal and mechanical properties of the molecular and binary ices suggest a larger range of phenomena than previously anticipated, sufficiently complex perhaps to account for many of the unusual geologic phenomena found on the icy satellites
Iapetus: Tectonic structure and geologic history
Many papers have been written about the surface of Iapetus, but most of these have discussed either the nature of the strongly contrasting light and dark materials or the cratering record. Little has been said about other geologic features on Iapetus, such as tectonic structures, which would provide constraints on Iapetus' thermal history. Most references have suggested that there is no conclusive evidence for any tectonic activity, even when thermal history studies indicate that there should be. However, a new study of Iapetus' surface involving the use of stereo pairs, an extensive tectonic network has been recognized. A few new observations concerning the craters and dark material were also made. Thus the geology and geologic history of Iapetus can be more fully outlined than before. The tectonic network is shown along with prominent craters and part of the dark material in the geologic/tectonic sketch map. The topology of crater rims and scarps are quite apparent and recognizable in the different image pairs. The heights and slopes of various features given are based on comparison with the depths of craters 50 to 100 km in diameter, which are assumed to have the same depths as craters of similar diameter on Rhea and Titania
Crater morphology and morphometry on the Uranian satellites
Fresh craters on the icy Uranian satellites exhibit a range of morphologies similar to craters on the icy satellites of Jupiter and Saturn. The general structural features found in the craters are described. Estimates of transition diameters from simple to complex crater morphologies are given for the five large Uranian satellites and 1985U1, and plotted with transition diameters on other bodies against surface gravity. Possible large-scale impacts are discussed
Beaming effect from increased-index photonic crystal waveguides
We study the beaming effect of light for the case of increased-index photonic
crystal (PhC) waveguides, formed through the omission of low-dielectric media
in the waveguide region. We employ the finite-difference time-domain numerical
method for characterizing the beaming effect and determining the mechanisms of
loss and the overall efficiency of the directional emission. We find that,
while this type of PhC waveguides is capable of producing a highly collimated
emission as was demonstrated experimentally, the inherent characteristics of
the structure result in a restrictively low efficiency in the coupling of light
into the collimated beam of light.Comment: 4 pages, 5 figures, submitted to Applied Physics
- …