21,322 research outputs found
Flare gamma ray continuum emission from neutral pion decay
We investigate, in detail, the production of solar flare gamma ray emission above 100 MeV via the interaction of high energy protons with the ambient solar atmosphere. We restrict our considerations to the broadband gamma ray spectrum resulting from the decay of neutral pions produced in p-H reactions. Thick-target calculations are performed to determine the photon fluences. However, proton transport is not considered. Inferences about the form of the proton spectrum at 10-100 MeV have already been drawn from de-excitation gamma ray lines. Our aim is to constrain the proton spectrum at higher energies. Thus, the injected proton spectrum is assumed to have the form of a Bessel Function, characteristics of stochastic energy at higher energies. The detailed shape of the gamma ray spectra around 100 MeV is found to have a strong dependence on the spectral index of the power law and on the turnover energy (from Bessel function to power law). As would be expected, the harder the photon spectrum the wider the 100 MeV feature. The photon spectra are to be compared with observations and used to place limits upon the number of particles accelerated and to constrain acceleration models
Introduction of interactive learning into French university physics classrooms
We report on a project to introduce interactive learning strategies (ILS) to
physics classes at the Universit\'e Pierre et Marie Curie (UPMC), one of the
leading science universities in France. In Spring 2012, instructors in two
large introductory classes, first-year, second-semester mechanics, and
second-year introductory E&M, enrolling approximately 500 and 250 students
respectively, introduced ILS into some sections of each class. The specific ILS
utilized were Think-Pair-Share questions and Peer Instruction in the main
lecture classrooms, and UW Tutorials for Introductory Physics in recitation
sections. Pre- and post-instruction assessments (FCI and CSEM respectively)
were given, along with a series of demographics questions. We were able to
compare the results of the FCI and CSEM between interactive and non-interactive
classes taught simultaneously with the same curriculum. We also analyzed final
exam results, as well as the results of student and instructor attitude surveys
between classes. In our analysis, we argue that Multiple Linear Regression
modeling is superior to other common analysis tools, including normalized gain.
Our results show that ILS are effective at improving student learning by all
measures used: research-validated concept inventories and final exam scores, on
both conceptual and traditional problem-solving questions. Multiple Linear
Regression analysis reveals that interactivity in the classroom is a
significant predictor of student learning, showing a similar or stronger
relationship with student learning than such ascribed characteristics as
parents' education, and achieved characteristics such as GPA and hours studied
per week. Analysis of student and instructors attitudes shows that both groups
believe that ILS improve student learning in the physics classroom, and
increases student engagement and motivation
A New Phenomenon: Sub-Tg, Solid-State, Plasticity-Induced Bonding in Polymers
Polymer self-adhesion due to the interdiffusion of macromolecules has been an
active area of research for several decades [70, 43, 62, 42, 72, 73, 41]. Here,
we report a new phenomenon of sub-Tg, solid-state, plasticity-induced bonding;
where amorphous polymeric films were bonded together in a period of time on the
order of a second in the solid-state at ambient temperatures nearly 60 K below
their glass transition temperature (Tg) by subjecting them to active plastic
deformation. Despite the glassy regime, the bulk plastic deformation triggered
the requisite molecular mobility of the polymer chains, causing
interpenetration across the interfaces held in contact. Quantitative levels of
adhesion and the morphologies of the fractured interfaces validated the sub-Tg,
plasticity-induced, molecular mobilization causing bonding. No-bonding outcomes
(i) during the compression of films in a near hydrostatic setting (which
inhibited plastic flow) and (ii) between an 'elastic' and a 'plastic' film
further established the explicit role of plastic deformation in this newly
reported sub-Tg solid-state bonding
Computational Study of the Structure and Thermodynamic Properties of Ammonium Chloride Clusters Using a Parallel J-Walking Approach
The thermodynamic and structural properties of (NHCl) clusters,
n=3-10 are studied. Using the method of simulated annealing, the geometries of
several isomers for each cluster size are examined. Jump-walking Monte Carlo
simulations are then used to compute the constant-volume heat capacity for each
cluster size over a wide temperature range. To carry out these simulations a
new parallel algorithm is developed using the Parallel Virtual Machine (PVM)
software package. Features of the cluster potential energy surfaces, such as
energy differences among isomers and rotational barriers of the ammonium ions,
are found to play important roles in determining the shape of the heat capacity
curves.Comment: Journal of Chemical Physics, accepted for publicatio
Stability of a Giant Connected Component in a Complex Network
We analyze the stability of the network's giant connected component under
impact of adverse events, which we model through the link percolation.
Specifically, we quantify the extent to which the largest connected component
of a network consists of the same nodes, regardless of the specific set of
deactivated links. Our results are intuitive in the case of single-layered
systems: the presence of large degree nodes in a single-layered network ensures
both its robustness and stability. In contrast, we find that interdependent
networks that are robust to adverse events have unstable connected components.
Our results bring novel insights to the design of resilient network topologies
and the reinforcement of existing networked systems
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