210 research outputs found
Challenging Endocrinology Students with a Critical Thinking Workbook
This is the accepted manuscript of an article published in Advances in Physiology Education. The version of record can be found here: https://doi.org/10.1152/advan.00101.2019A central goal of science education is to help students develop higher order thinking skills to enable them to face the challenges of life. Accordingly, science instructors are now urged to craft their classrooms such that they serve not only as spaces for disseminating information, but also an arena through which students are encouraged to think scientifically and develop critical thinking skills. This project aimed to develop a workbook that helps postsecondary students learn endocrinology and engages them in critical thinking. Each of the five chapters focus on a different topic rooted within core biological concepts relevant to endocrinology. Such topics were identified upon cross referencing seminal reports on science education. Tenants of Numrich’s Sequence of Critical Thinking Tasks were used to guide the development of chapter sections with the intent of engaging students in critical thinking over time by way of practice and scaffolded guidance. Chapter sections include modeling, event sequencing, clinical application, research and communication, and simulation, each of which target a different repertoire of skills presented in Numrich’s framework. Students’ learning, experiences, and behaviors were used to evaluate the workbook and inform the revision of the workbook into the publicly-available second edition
Dynamics of a ferromagnetic domain wall and the Barkhausen effect
We derive an equation of motion for the the dynamics of a ferromagnetic
domain wall driven by an external magnetic field through a disordered medium
and we study the associated depinning transition. The long-range dipolar
interactions set the upper critical dimension to be , so we suggest that
mean-field exponents describe the Barkhausen effect for three-dimensional soft
ferromagnetic materials. We analyze the scaling of the Barkhausen jumps as a
function of the field driving rate and the intensity of the demagnetizing
field, and find results in quantitative agreement with experiments on
crystalline and amorphous soft ferromagnetic alloys.Comment: 4 RevTex pages, 3 ps figures embedde
First direct observation of Dirac fermions in graphite
Originating from relativistic quantum field theory, Dirac fermions have been
recently applied to study various peculiar phenomena in condensed matter
physics, including the novel quantum Hall effect in graphene, magnetic field
driven metal-insulator-like transition in graphite, superfluid in 3He, and the
exotic pseudogap phase of high temperature superconductors. Although Dirac
fermions are proposed to play a key role in these systems, so far direct
experimental evidence of Dirac fermions has been limited. Here we report the
first direct observation of massless Dirac fermions with linear dispersion near
the Brillouin zone (BZ) corner H in graphite, coexisting with quasiparticles
with parabolic dispersion near another BZ corner K. In addition, we report a
large electron pocket which we attribute to defect-induced localized states.
Thus, graphite presents a novel system where massless Dirac fermions,
quasiparticles with finite effective mass, and defect states all contribute to
the low energy electronic dynamics.Comment: Nature Physics, in pres
Modern Electronic Techniques Applied to Physics and Engineering
Contains reports on two research projects
Detecting sterile dark matter in space
Space-based instruments provide new and, in some cases, unique opportunities
to search for dark matter. In particular, if dark matter comprises sterile
neutrinos, the x ray detection of their decay line is the most promising
strategy for discovery. Sterile neutrinos with masses in the keV range could
solve several long-standing astrophysical puzzles, from supernova asymmetries
and the pulsar kicks to star formation, reionization, and baryogenesis. The
best current limits on sterile neutrinos come from Chandra and XMM-Newton.
Future advances can be achieved with a high-resolution x-ray spectrometry in
space.Comment: 11 pages, 1 figure, to appear in proceedings "From Quantum to Cosmos:
fundametal physics research in space", Washington, DC, May 22-24, 200
Dynamics of a ferromagnetic domain wall: avalanches, depinning transition and the Barkhausen effect
We study the dynamics of a ferromagnetic domain wall driven by an external
magnetic field through a disordered medium. The avalanche-like motion of the
domain walls between pinned configurations produces a noise known as the
Barkhausen effect. We discuss experimental results on soft ferromagnetic
materials, with reference to the domain structure and the sample geometry, and
report Barkhausen noise measurements on FeCoB amorphous
alloy. We construct an equation of motion for a flexible domain wall, which
displays a depinning transition as the field is increased. The long-range
dipolar interactions are shown to set the upper critical dimension to ,
which implies that mean-field exponents (with possible logarithmic correction)
are expected to describe the Barkhausen effect. We introduce a mean-field
infinite-range model and show that it is equivalent to a previously introduced
single-degree-of-freedom model, known to reproduce several experimental
results. We numerically simulate the equation in , confirming the
theoretical predictions. We compute the avalanche distributions as a function
of the field driving rate and the intensity of the demagnetizing field. The
scaling exponents change linearly with the driving rate, while the cutoff of
the distribution is determined by the demagnetizing field, in remarkable
agreement with experiments.Comment: 17 RevTeX pages, 19 embedded ps figures + 1 extra figure, submitted
to Phys. Rev.
A Survey of OH Masers Towards High Mass Protostellar Objects
We present a survey of OH maser emission towards a sample of high mass
protostellar objects made using the Nancay and GBT telescopes.OH maser emission
was detected towards 63 objects with 36 new detections. There are 56
star-forming regions and 7 OH/IR candidates. There is no evidence that sources
with OH masers have a different range of luminosities from the non-maser
sources. The results of this survey are compared with previous water and class
II methanol maser observations of the same objects. Some of the detected
sources are only associated with OH masers and some sources are only associated
with the 1720 MHz OH maser line. The velocity range of the maser emission
suggests that the water maser sources may be divided into two groups. The
detection rates and velocity range of the OH and Class II methanol masers
support the idea that there is a spatial association of the OH and Class II
methanol masers. The sources span a wide range in R, the ratio of the methanol
maser peak flux to OH 1665 MHz maser peak flux, however there are only a few
sources with intermediate values of R, 8<R<32, which has characterised previous
samples. Sources which have masers of any species, OH, water or methanol, have
redder [100um-12um] IRAS colours than those without masers. However, there is
no evidence for different maser species tracing different stages in the
evolution of these young high mass sources. Previous observations which have
shown that the OH maser emission from similar sources traces the circumstellar
disks around the objects. This combined with the sensitivity of the OH emission
to the magnetic field, make the newly detected sources interesting candidates
for future follow-up at high angular resolution.Comment: Accepted for publication in A&
Modern Electronic Techniques Applied to Physics and Engineering
Contains reports on seven research projects.Office of Scientific Research and Development (OSRD) OEMsr-26
Visualizing the Anthropocene dialectically: Jessica Woodworth and Peter Brosens’ eco-crisis trilogy
The ambition of this article is to propose a way of visualizing the Anthropocene dialectically. As suggested by the Dutch atmospheric chemist Paul Crutzen and the professor of biology Eugene F. Stoermer, the term Anthropocene refers to a historical period in which humankind has turned into a geological force that transforms the natural environment in such a way that it is hard to distinguish between the human and the natural world. Crutzen and Stoermer explain that the Anthropocene has begun after the Holocene, the geological epoch that followed the last ice age and lasted until the industrial revolution. Drawing on a number of figures such as the “tenfold” increase in urbanisation, the extreme transformation of land surface by human action, the use of more than 50% of all accessible fresh water by humans, and the massive increase in greenhouse emissions, Crutzen and Stoermer conclude that the term Anthropocene describes aptly mankind's influence on ecological and geological cycles (Crutzen & Stoermer, 2000, p.17). The wager of this article is that we need to identify ways to visualize the Anthropocene dialectically and I proceed to do so using as a case study Jessica Woodworth's and Peter Brosen's trilogy on the conflict between humans and nature, which consists of Khadak (2006), Altiplano (2009), and The Fifth Season (La Cinquième Saison, 2012)
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