1,422 research outputs found
Ultraviolet absorption by interstellar gas at large distances from the galactic plane
Eighteen high dispersion International Ultraviolet Exploration spectra of 6 stars in the large magellanic cloud (LMC) 3 stars in the small magellanic cloud (SMC) and 2 foreground stars were studied. Fourteen spectra cover the wavelengths lambda 1150-2000 A and 4 cover lambda 1900-3200 A. All the Magellanic Cloud star spectra exhibit exceedingly strong interstellar absorption lines due to a wide range of ionization stages at galactic velocities and at velocities associated with the LMC or SMC. The analysis is restricted to the Milky Way absorption features. Toward the LMC stars, the strong interstellar lines have a positive velocity extension, which exceeds the extension recorded toward the SMC stars. The most straightforward interpretation of these velocity extensions is obtained by assuming that gas at large distances away from the plane of the galaxy participates in the rotation of the galaxy as found in the galactic disk
The CLA+ and the Two Cultures: Writing Assessment and Educational Testing
The CLA+ and the Two Cultures: Writing Assessment and Educational Testing concerns the Collegiate Learning Assessment+, a standardized test of collegiate learning currently being piloted at Purdue, and its potential impacts on writing programs and pedagogy. From an empirical, theoretical, and historical perspective, I consider the test as an assessment of writing and college learning, and use it as a lens through which to understand traditional antagonisms between writing instructors and the educational testing industry. My research details the institutional and political conditions that led to the rise of the standardized assessment movement nationally and locally, and analyzes results from Purdue\u27s piloting program for the test. I argue that literacy educators must adapt to the increasing prevalence of standardized testing at the collegiate level in a way that preserves our independence and autonomy, and that if undertaken with care this adaptation need not jeopardize our traditional ideals
Setting the record straight on precision agriculture adoption
There is a perception that adoption of precision agriculture (PA) has been slow. This study reviews the public data on farm level use of PA in crop production worldwide. It examines adoption estimates for PA from completed surveys that utilized random sampling procedures, as well as estimates of adoption using other survey methods, with an objective to document the national or regional level adoption patterns of PA using existing data. The analysis indicates that Global Navigation Satellite Systems (GNSS) guidance and associated automated technologies like sprayer boom control and planter row or section shutoffs have been adopted as fast as any major agricultural technology in history. The main reason for the perception that PA adoption is slow is because PA is often associated with variable rate technology (VRT)—just one of many PA technologies, one of the first adopted by many farmers, but that now rarely exceeds 20% of farms. This level of adoption suggests that farmers like the idea of VRT, but are not convinced of its value. VRT adoption estimates for niche groups of farmers may exceed 50%. The biggest gap in PA adoption is for medium and small farms in the developing world that do not use motorized mechanization
Profitable chemical-free cowpea storage technology for smallholder farmers in Africa: opportunities and challenges
Cowpea is the most economically and nutritionally important indigenous African grain legume, grown by millions of resource-poor farmers. It is a key cash crop in areas too dry to grow cotton or other export crops. Most of the over 3 million t of cowpea grain produced annually in West and Central Africa is grown on small farms. Storage is often identified as the key challenge for small scale cowpea growers. Many farmers sell cowpea grain at low harvest time prices rather than risk losses by bruchids during storage. Some traditional methods are effective for small quantities (e.g., 10 kg), but are difficult to scale up. Some effective storage chemicals are available, but they are regularly misused by farmers and merchants. The Purdue Improved Cowpea Storage (PICS) Project is addressing these problems through promotion of hermetic storage in triple layer sacks which have an outer layer of woven polypropylene and two liners of 80 μ high-density polyethylene. Village demonstrations with more than 45, 000 PICS sacks have shown the technology to be effective. Good quality affordable sacks have been produced by manufacturers in Nigeria, Burkina Faso and Mali. Over the past three years more than one million sacks have been produced and sold. Despite the success with the outreach activities and the farmer adoption, the challenge remains to develop sustainable sack distribution networks. Issues identified include reluctance of wholesalers to order sacks due to risk associated with a new product, inability of wholesalers to develop effective distribution networks due to difficulties with enforcing contracts, and limited access to capital. The PICS project is exploring new ways to address some of these issues, including using non-traditional distribution systems for PICS sacks such as agro-dealers networks, and adapting distribution systems that have worked for cell phones and other products. Keywords: Cowpea, Bruchids, Hermetic storage, Supply chain, West and Central Afric
Stochastic Feedback and the Regulation of Biological Rhythms
We propose a general approach to the question of how biological rhythms
spontaneously self-regulate, based on the concept of ``stochastic feedback''.
We illustrate this approach by considering the neuroautonomic regulation of the
heart rate. The model generates complex dynamics and successfully accounts for
key characteristics of cardiac variability, including the power spectrum,
the functional form and scaling of the distribution of variations, and
correlations in the Fourier phases. Our results suggest that in healthy systems
the control mechanisms operate to drive the system away from extreme values
while not allowing it to settle down to a constant output.Comment: 15 pages, latex2e using rotate and epsf, with 4 ps figures. Submitted
to PR
Analytic Detection Thresholds for Measurements of Linearly Polarized Intensity Using Rotation Measure Synthesis
A fully analytic statistical formalism does not yet exist to describe
radio-wavelength measurements of linearly polarized intensity that are produced
using rotation measure synthesis. In this work we extend the analytic formalism
for standard linear polarization, namely that describing measurements of the
quadrature sum of Stokes Q and U intensities, to the rotation measure synthesis
environment. We derive the probability density function and expectation value
for Faraday-space polarization measurements for both the case where true
underlying polarized emission is present within unresolved Faraday components,
and for the limiting case where no such emission is present. We then derive
relationships to quantify the statistical significance of linear polarization
measurements in terms of standard Gaussian statistics. The formalism developed
in this work will be useful for setting signal-to-noise ratio detection
thresholds for measurements of linear polarization, for the analysis of
polarized sources potentially exhibiting multiple Faraday components, and for
the development of polarization debiasing schemes.Comment: 14 pages, 6 figures, accepted for publication in MNRA
New ANCs for synthesis obtained using extrapolation method and the -factor for radiative capture
Background: The O reaction, determining the
survival of carbon in red giants, is of interest for nuclear reaction theory
and nuclear astrophysics. Numerous attempts to obtain the astrophysical factor
of the O reaction, both experimental and
theoretical, have been made for almost 50 years. The specifics of the O
nuclear structure is the presence of two subthreshold bound states, (6.92 MeV,
2) and (7.12 MeV, 1), dominating the behavior of the low-energy
-factor. The strength of these subthreshold states is determined by their
asymptotic normalization coefficients (ANCs) which need to be known with high
accuracy. Recently, using the model-independent extrapolation method,
Blokhintsev {\it et al.} [Eur. Phys. J. A {\bf 59}, 162 (2023)] determined the
ANCs for the three subthreshold states in O.
Purpose: In this paper, using these newly determined ANCs, we calculated the
low-energy astrophysical -factors for the O radiative capture.
Method: The -factors are calculated within the framework of the -matrix
method using the AZURE2 code.
Conclusion: Our total -factor includes the resonance and
transitions to the ground state of O interfering with the corresponding
direct captures and cascade radiative captures to the ground state of O
through four subthreshold states: and . Since our
ANCs are higher than those used by deBoer {\it et al.} [Rev. Mod. Phys. {\bf
89}, 035007 (2017)], the present total -factor at the most effective
astrophysical energy of 300 keV is 174 keVb versus 137 keVb of that work.
Accordingly, our calculated reaction rate at low temperatures () is
higher than the one given in the aforesaid paper
COMPTEL observations of the inner galaxy
This paper presents a first global study of COMPTEL observations of the inner Galaxy in the energy range 0.75–10 MeV. Preliminary findings demonstrate COMPTEL’s capabilities for mapping the observed gamma radiation and disentangling the contributions from point sources and diffuse emission
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