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Oxygen isotopic and petrological constraints on the origin and relationship of IIE iron meteorites and H chondrites
New oxygen isotopic measurements of IIEs and H chondrites are indistinguishable — strengthening a possible common origin for these groups. Combining oxygen results with mineralogy, the nature of their parent body or bodies can be explored
Learning physics in context: a study of student learning about electricity and magnetism
This paper re-centres the discussion of student learning in physics to focus
on context. In order to do so, a theoretically-motivated understanding of
context is developed. Given a well-defined notion of context, data from a novel
university class in electricity and magnetism are analyzed to demonstrate the
central and inextricable role of context in student learning. This work sits
within a broader effort to create and analyze environments which support
student learning in the sciencesComment: 36 pages, 4 Figure
Characterizing Different Motility Induced Regimes in Active Matter with Machine Learning and Noise
We examine motility-induced phase separation (MIPS) in two-dimensional run
and tumble disk systems using both machine learning and noise fluctuation
analysis. Our measures suggest that within the MIPS state there are several
distinct regimes as a function of density and run time, so that systems with
MIPS transitions exhibit an active fluid, an active crystal, and a critical
regime. The different regimes can be detected by combining an order parameter
extracted from principal component analysis with a cluster stability
measurement. The principal component-derived order parameter is maximized in
the critical regime, remains low in the active fluid, and has an intermediate
value in the active crystal regime. We demonstrate that machine learning can
better capture dynamical properties of the MIPS regimes compared to more
standard structural measures such as the maximum cluster size. The different
regimes can also be characterized via changes in the noise power of the
fluctuations in the average speed. In the critical regime, the noise power
passes through a maximum and has a broad spectrum with a signature,
similar to the noise observed near depinning transitions or for solids
undergoing plastic deformation.Comment: 11 pages, 9 figure
Dynamic regimes for driven colloidal particles on a periodic substrate at commensurate and incommensurate fillings
We numerically examine colloidal particles driven over a muffin tin substrate. Previous studies of this model identified a variety of commensurate and incommensurate static phases in which topological defects can form domain walls, ordered stripes, superlattices, or disordered patchy regimes as a function of the filling fraction. Here, we show that the addition of an external drive to these static phases can produce distinct dynamical responses. At incommensurate fillings the flow occurs in the form of localized pulses or solitons correlated with topological defect structures. Transitions between different modes of motion can occur as a function of increasing drive. We measure the average particle velocity for specific ranges of external drive and show that changes in the velocity response correlate with changes in the topological defect arrangements. We also demonstrate that in the different dynamic phases, the particles have distinct trajectories and velocity distributions. Dynamic transitions between ordered and disordered flows exhibit hysteresis, while in strongly disordered regimes there is no hysteresis and the velocity-force curves are smooth. When stripe patterns are present, transport can occur at an angle to the driving direction
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