472 research outputs found
From multiple perspectives to shared understanding
The aim of this study was to explore how learners operating in a small group reach shared understanding as they work out joint research questions and build a theoretical framework and to identify the resources and tools they used in the process. The learnersâ own interpretations of their group activities and learning were also taken into account. The data, consisting of group discussions and the documents produced by the group, were subjected to a qualitative content analysis. The group members employed a variety of resources and tools to exchange their individual perspectives and achieve shared understanding. Summaries of relevant literature laid a foundation for the groupâs theoretical discussions. Reflective comparisons between their book knowledge and their personal experiences of online interaction and collaboration were frequent, suggesting that such juxtapositions may have enhanced their learning by intertwining the content to be mastered and the activities entailed by this particular content
Beta-delayed-neutron studies of Sb and I performed with trapped ions
Beta-delayed-neutron (n) spectroscopy was performed using the
Beta-decay Paul Trap and an array of radiation detectors. The n
branching ratios and energy spectra for Sb and I were
obtained by measuring the time of flight of recoil ions emerging from the
trapped ion cloud. These nuclei are located at the edge of an isotopic region
identified as having n branching ratios that impact the r-process
abundance pattern around the A~130 peak. For Sb and I,
n branching ratios of 14.6(11)%, 17.6(28)%, and 7.6(28)% were
determined, respectively. The n energy spectra obtained for Sb
and I are compared with results from direct neutron measurements, and
the n energy spectrum for Sb has been measured for the first
time
Scintillation efficiency measurement of Na recoils in NaI(Tl) below the DAMA/LIBRA energy threshold
The dark matter interpretation of the DAMA modulation signal depends on the
NaI(Tl) scintillation efficiency of nuclear recoils. Previous measurements for
Na recoils have large discrepancies, especially in the DAMA/LIBRA modulation
energy region. We report a quenching effect measurement of Na recoils in
NaI(Tl) from 3keV to 52keV, covering the whole
DAMA/LIBRA energy region for light WIMP interpretations. By using a low-energy,
pulsed neutron beam, a double time-of-flight technique, and pulse-shape
discrimination methods, we obtained the most accurate measurement of this kind
for NaI(Tl) to date. The results differ significantly from the DAMA reported
values at low energies, but fall between the other previous measurements. We
present the implications of the new quenching results for the dark matter
interpretation of the DAMA modulation signal
Vegetarian Dietary Patterns Are Associated With a Lower Risk of Metabolic Syndrome: The Adventist Health Study 2
Validation of self-reported anthropometrics in the Adventist Health Study 2
<p>Abstract</p> <p>Background</p> <p>Relying on self-reported anthropometric data is often the only feasible way of studying large populations. In this context, there are no studies assessing the validity of anthropometrics in a mostly vegetarian population. The objective of this study was to evaluate the validity of self-reported anthropometrics in the Adventist Health Study 2 (AHS-2).</p> <p>Methods</p> <p>We selected a representative sample of 911 participants of AHS-2, a cohort of over 96,000 adult Adventists in the USA and Canada. Then we compared their measured weight and height with those self-reported at baseline. We calculated the validity of the anthropometrics as continuous variables, and as categorical variables for the definition of obesity.</p> <p>Results</p> <p>On average, participants underestimated their weight by 0.20 kg, and overestimated their height by 1.57 cm resulting in underestimation of body mass index (BMI) by 0.61 kg/m<sup>2</sup>. The agreement between self-reported and measured BMI (as a continuous variable), as estimated by intraclass correlation coefficient, was 0.97. The sensitivity of self-reported BMI to detect obesity was 0.81, the specificity 0.97, the predictive positive value 0.93, the predictive negative value 0.92, and the Kappa index 0.81. The percentage of absolute agreement for each category of BMI (normoweight, overweight, and obese) was 83.4%. After multivariate analyses, predictors of differences between self-reported and measured BMI were obesity, soy consumption and the type of dietary pattern.</p> <p>Conclusions</p> <p>Self-reported anthropometric data showed high validity in a representative subsample of the AHS-2 being valid enough to be used in epidemiological studies, although it can lead to some underestimation of obesity.</p
Non linear pseudo-bosons versus hidden Hermiticity. II: The case of unbounded operators
Parallels between the notions of nonlinear pseudobosons and of an apparent
non-Hermiticity of observables as shown in paper I (arXiv: 1109.0605) are
demonstrated to survive the transition to the quantum models based on the use
of unbounded metric in the Hilbert space of states.Comment: 21 p
Low-lying level structure of Cu and its implications on the rp process
The low-lying energy levels of proton-rich Cu have been extracted
using in-beam -ray spectroscopy with the state-of-the-art -ray
tracking array GRETINA in conjunction with the S800 spectrograph at the
National Superconducting Cyclotron Laboratory at Michigan State University.
Excited states in Cu serve as resonances in the
Ni(p,)Cu reaction, which is a part of the rp-process in
type I x-ray bursts. To resolve existing ambiguities in the reaction Q-value, a
more localized IMME mass fit is used resulting in ~keV. We derive
the first experimentally-constrained thermonuclear reaction rate for
Ni(p,)Cu. We find that, with this new rate, the
rp-process may bypass the Ni waiting point via the Ni(p,)
reaction for typical x-ray burst conditions with a branching of up to
40. We also identify additional nuclear physics uncertainties that
need to be addressed before drawing final conclusions about the rp-process
reaction flow in the Ni region.Comment: 8 pages, accepted for Phys. Rev.
IShTAR: a test facility to study the interaction between RF wave and edge plasmas
International audienceExistence of high electric fields near an RF antenna launcher causes a number of parasitic phenomena, such as arcing and impurity release, which seriously deteriorate the performance of an ICRF heating scheme in fusion devices. Limited accessibility of the near antenna region in large-scale fusion experiments significantly complicates the associated experimental studies. The IShTAR (Ion Sheath Test Arrangement) test facility has been developed with the requirement to provide a better accessibility and diagnosability of plasmas in the direct vicinity of an ICRF antenna. The purpose of this work is to give a detailed description on the experimental setup and the available diagnostics. Furthermore the paper will demonstrate the capability of the experiment to study phenomena near an ICRF antenna launcher which are relevant for large-scale fusion ICRH systems
Measurement of Scintillation and Ionization Yield and Scintillation Pulse Shape from Nuclear Recoils in Liquid Argon
We have measured the scintillation and ionization yield of recoiling nuclei
in liquid argon as a function of applied electric field by exposing a
dual-phase liquid argon time projection chamber (LAr-TPC) to a low energy
pulsed narrow band neutron beam produced at the Notre Dame Institute for
Structure and Nuclear Astrophysics. Liquid scintillation counters were arranged
to detect and identify neutrons scattered in the TPC and to select the energy
of the recoiling nuclei. We report measurements of the scintillation yields for
nuclear recoils with energies from 10.3 to 57.3 keV and for median applied
electric fields from 0 to 970 V/cm. For the ionization yields, we report
measurements from 16.9 to 57.3 keV and for electric fields from 96.4 to 486
V/cm. We also report the observation of an anticorrelation between
scintillation and ionization from nuclear recoils, which is similar to the
anticorrelation between scintillation and ionization from electron recoils.
Assuming that the energy loss partitions into excitons and ion pairs from
Kr internal conversion electrons is comparable to that from Bi
conversion electrons, we obtained the numbers of excitons () and ion
pairs () and their ratio () produced by nuclear recoils from
16.9 to 57.3 keV. Motivated by arguments suggesting direction sensitivity in
LAr-TPC signals due to columnar recombination, a comparison of the light and
charge yield of recoils parallel and perpendicular to the applied electric
field is presented for the first time.Comment: v2 to reflect published versio
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