5,101 research outputs found
Cavitation Scaling Experiments with Axisymmetric Bodies
Several experiments by Ceccio and Brennen (1991, 1989) and Kumar and Brennen (1992, 1991) have closely examined the interaction between individual cavitation bubbles and the boundary layer, as well as statistical properties of the acoustical signals produced by the bubble collapse. All of these experiments were, however, conducted in the same facility with the same headform size (5.08cm in diameter) and over a fairly narrow range of flow velocities (around 9m/s). Clearly this raises the issue of how the phenomena identified change with speed, scale and facility. The present paper describes experiments conducted in order to try to answer some of these important questions regarding the scaling of the cavitation phenomena. The experiments were conducted in the Large Cavitation Channel of the David Taylor Research Center in Memphis Tennessee, on geometrically similar Schiebe headforms which are 5.08, 25.4 and 50.8cm in diameter for speeds ranging up to 15m/s and for a range of cavitation numbers
Irrational vs. rational charge and statistics in two-dimensional quantum systems
We show that quasiparticle excitations with irrational charge and irrational
exchange statistics exist in tight-biding systems described, in the continuum
approximation, by the Dirac equation in (2+1)-dimensional space and time. These
excitations can be deconfined at zero temperature, but when they are, the
charge re-rationalizes to the value 1/2 and the exchange statistics to that of
"quartons" (half-semions).Comment: 4 pages, 2 figure
The Environments around Long-Duration Gamma-Ray Burst Progenitors
Gamma-ray burst (GRB) afterglow observations have allowed us to significantly
constrain the engines producing these energetic explosions. Te redshift and
position information provided by these afterglows have already allowed us to
limit the progenitors of GRBs to only a few models. The afterglows may also
provide another observation that can place further constraints on the GRB
progenitor: measurements telling us about the environments surrounding GRBs.
Current analyses of GRB afterglows suggest that roughly half of long-duration
gamma-ray bursts occur in surroundings with density profiles that are uniform.
We study the constraints placed by this observation on both the classic
``collapsar'' massive star progenitor and its relative, the ``helium-merger''
progenitor. We study several aspects of wind mass-loss and find that our
modifications to the standard Wolf-Rayet mass-loss paradigm are not sufficient
to produce constant density profiles. Although this does not rule out the
standard ``collapsar'' progenitor, it does suggest a deficiency with this
model. We then focus on the He-merger models and find that such progenitors can
fit this particular constraint well. We show how detailed observations can not
only determine the correct progenitor for GRBs, but also allow us to study
binary evolution physics.Comment: 44 pages including 11 figure
Mean shear flows generated by nonlinear resonant Alfven waves
In the context of resonant absorption, nonlinearity has two different
manifestations. The first is the reduction in amplitude of perturbations around
the resonant point (wave energy absorption). The second is the generation of
mean shear flows outside the dissipative layer surrounding the resonant point.
Ruderman et al. [Phys. Plasmas 4, 75 (1997)] studied both these effects at the
slow resonance in isotropic plasmas. Clack et al. [Astron. Astrophys. 494}, 317
(2009)] investigated nonlinearity at the Alfven resonance, however, they did
not include the generation of mean shear flow. In this present paper, we
investigate the mean shear flow, analytically, and study its properties. We
find that the flow generated is parallel to the magnetic surfaces and has a
characteristic velocity proportional to , where is
the dimensionless amplitude of perturbations far away from the resonance. This
is, qualitatively, similar to the flow generated at the slow resonance. The
jumps in the derivatives of the parallel and perpendicular components of mean
shear flow across the dissipative layer are derived. We estimate the generated
mean shear flow to be of the order of in both the solar
upper chromosphere and solar corona, however, this value strongly depends on
the choice of boundary conditions. It is proposed that the generated mean shear
flow can produce a Kelvin--Helmholtz instability at the dissipative layer which
can create turbulent motions. This instability would be an additional effect,
as a Kelvin--Helmholtz instability may already exist due to the velocity field
of the resonant Alfven waves. This flow can also be superimposed onto existing
large scale motions in the solar upper atmosphere.Comment: 11 page
Pathways to Careers in Health Care
The Patient Protection and Affordable Care Act passed by Congress and signed into law by President Barack Obama in 2010 effected major changes in the financing and delivery of health care in the United States. It also authorized creation of the Health Profession Opportunity Grants program (HPOG), a demonstration effort within the U.S. Department of Health and Human Services to provide opportunities for education and training that lead to jobs and career advancement in health care for recipients of Temporary Assistance for Needy Families (TANF) and other low-income individuals and to respond to the increasing demand for health care professionals. As a demonstration program, HPOG also featured a mandated federal evaluation to assess its success and a corresponding research programâthe HPOG University Partnership Research Grants (HPOG UP), a collaborative effort between the program operators and academic researchers from different disciplinesâto observe various aspects of its operations.
HPOG unites two important innovations in workforce development programming for serving low-income populations in recent decades, career pathways and sector strategies, by actively fostering the use of the former in the context of one major sectorâhealth care. Health care is one of the only sectors that continued to exhibit growth year after year in periods of general economic expansion as well as decline. Health care employment even continued to expand in most states and communities across the United States through the Great Recession in 2008â2009. In addition to offering insights into these strategies and their evolution, the authors in this book present the findings, lessons, and recommendations that emanated from HPOG research and evaluations for consideration by policymakers, program operators, and other researchers.https://research.upjohn.org/up_press/1279/thumbnail.jp
Curated Collections for Educators: Five Key Papers on Clinical Teaching
The ability to teach in the clinical setting is of paramount importance. Clinical teaching is at the heart of medical education, irrespective of the learnerâs level of training. Learners desire and need effective, competent, and thoughtful clinical teaching from their instructors. However, many clinician-educators lack formal training on this important skill and thus may provide a variable experience to their learners. Although formal training of clinician-educators is standard and required in many other countries, the United States has yet to follow suit, leaving many faculty members to fend for themselves to learn these important skills.
In September 2018, the Academic Life in Emergency Medicine (ALiEM) 2018-2019 Faculty Incubator program discussed the topic of clinical teaching techniques. We gathered the titles of papers that were cited, shared, and recommended within our online discussion forum and compiled the articles pertaining to the topic of clinical teaching techniques. To augment the list, the authors did a formal literature search using the search terms âteaching techniques", "clinical teaching", "medical education", "medical students", and "residentsâ on Google Scholar and PubMed. Finally, we posted a call for important papers on the topic of clinical teaching techniques on Twitter.
Through this process, we identified 48 core articles on the topic of clinical teaching. We conducted a modified Delphi methodology to identify the key papers on the topic. In this paper, we present the five highest-rated articles based on the relevance to junior faculty and faculty developers. This article will review and summarize the articles we found to be the most impactful to improve oneâs clinical teaching skills
Evidence for a supermassive object in the nucleus of the galaxy M87 from SIT and CCD area photometry
Two-dimensional SIT and CCD detectors have been used to measure the surface brightness of the peculiar elliptical radio galaxy M87. Measurements were made in three broad-band colors (B, V, and R) to a distance of 80" from the nucleus, with 1" spatial resolution and photometric
accuracy of the order of 1%. The data are given in some detail and are compared with earlier photographic results. The most obvious feature of the data is a bright, barely resolved central luminosity spike, which is not seen in similar data on other nearby normal ellipticals. Also, attempts to fit isothermal or King models away from the nuclear spike show additional excess luminosity in the central regions of the galaxy (r 60. All of the existing data is well fitted by a King model containing a central black hole of mass M = 3 x 10^9 M_â and a point
luminosity source. While such a model is not uniquely required by the data, it is perhaps the most plausible of several possible models considered. At present, M87 is probably the best case for a hypothetical massive black hole in a galaxy nucleus
- âŠ