4,392 research outputs found
Tuning Interparticle Hydrogen Bonding in Shear-Jamming Suspensions: Kinetic Effects and Consequences for Tribology and Rheology
The shear-jamming of dense suspensions can be strongly affected by
molecular-scale interactions between particles, e.g. by chemically controlling
their propensity for hydrogen bonding. However, hydrogen bonding not only
enhances interparticle friction, a critical parameter for shear jamming, but
also introduces (reversible) adhesion, whose interplay with friction in
shear-jamming systems has so far remained unclear. Here, we present atomic
force microscopy studies to assess interparticle adhesion, its relationship to
friction, and how these attributes are influenced by urea, a molecule that
interferes with hydrogen bonding. We characterize the kinetics of this process
with nuclear magnetic resonance, relating it to the time dependence of the
macroscopic flow behavior with rheological measurements. We find that
time-dependent urea sorption reduces friction and adhesion, causing a shift in
the shear-jamming onset. These results extend our mechanistic understanding of
chemical effects on the nature of shear jamming, promising new avenues for
fundamental studies and applications alike
Effect of the Coriolis Force on the Hydrodynamics of Colliding Wind Binaries
Using fully three-dimensional hydrodynamic simulations, we investigate the
effect of the Coriolis force on the hydrodynamic and observable properties of
colliding wind binary systems. To make the calculations tractable, we assume
adiabatic, constant velocity winds. The neglect of radiative driving,
gravitational deceleration, and cooling limit the application of our models to
real systems. However, these assumptions allow us to isolate the effect of the
Coriolis force, and by simplifying the calculations, allow us to use a higher
resolution (up to 640^3) and to conduct a larger survey of parameter space. We
study the dynamics of collidng winds with equal mass loss rates and velocities
emanating from equal mass stars on circular orbits, with a range of values for
the ratio of the wind to orbital velocity. We also study the dynamics of winds
from stars on elliptical orbits and with unequal strength winds. Orbital motion
of the stars sweeps the shocked wind gas into an Archimedean spiral, with
asymmetric shock strengths and therefore unequal postshock temperatures and
densities in the leading and trailing edges of the spiral. We observe the
Kelvin-Helmholtz instability at the contact surface between the shocked winds
in systems with orbital motion even when the winds are identical. The change in
shock strengths caused by orbital motion increases the volume of X-ray emitting
post-shock gas with T > 0.59 keV by 63% for a typical system as the ratio of
wind velocity to orbital velocity decreases to V_w/V_o = 2.5. This causes
increased free-free emission from systems with shorter orbital periods and an
altered time-dependence of the wind attenuation. We comment on the importance
of the effects of orbital motion on the observable properties of colliding wind
binaries.Comment: 12 pages, 17 figures, accepted for publication in Ap
Learning Focused Schools Strategies: The Level of Implementation and Perceived Impact on Student Achievement
Max Thompson’s Learning Focused Strategies approach to school improvement has been embraced by school leaders and teachers as an approach to redesign and reform public schools. The program developers claim schools with 90% minority students and 90% of students qualifying for free or reduced lunch programs can achieve at high levels on required curriculum. Examined are the beliefs and attitudes of teachers as related to the degree of implementation of Learning Focused Strategies in their classrooms. The study supported the premise that LFS are research based and effective, that teachers believe the strategies will improve instruction, high level of implementation, enhancing the potential for student success. The study examined the relationships between experience, grade level, degree level, and the self reported degree of implementation
Electroweak Bremsstrahlung in Dark Matter Annihilation
A conservative upper bound on the total dark matter (DM) annihilation rate
can be obtained by constraining the appearance rate of the annihilation
products which are hardest to detect. The production of neutrinos, via the
process , has thus been used to set a strong
general bound on the dark matter annihilation rate. However, Standard Model
radiative corrections to this process will inevitably produce photons which may
be easier to detect. We present an explicit calculation of the branching ratios
for the electroweak bremsstrahlung processes and
. These modes inevitably lead to electromagnetic
showers and further constraints on the DM annihilation cross-section. In
addition to annihilation, our calculations are also applicable to the case of
dark matter decay.Comment: 7 pages, 4 figures. New appendix with an extensive discussion of
Majorana fermions and helicity suppression
A Template Analysis of Intimate Partner Violence Survivors’ Experiences of Animal Maltreatment: Implications for Safety Planning and Intervention
This study explores the intersection of intimate partner violence (IPV) and animal cruelty in an ethnically diverse sample of 103 pet-owning IPV survivors recruited from community-based domestic violence programs. Template analysis revealed five themes: (a) Animal Maltreatment by Partner as a Tactic of Coercive Power and Control, (b) Animal Maltreatment by Partner as Discipline or Punishment of Pet, (c) Animal Maltreatment by Children, (d) Emotional and Psychological Impact of Animal Maltreatment Exposure, and (e) Pets as an Obstacle to Effective Safety Planning. Results demonstrate the potential impact of animal maltreatment exposure on women and child IPV survivors’ health and safety
Remembering Forward: Neural Correlates of Memory and Prediction in Human Motor Adaptation
We used functional MR imaging (FMRI), a robotic manipulandum and systems identification techniques to examine neural correlates of predictive compensation for spring-like loads during goal-directed wrist movements in neurologically-intact humans. Although load changed unpredictably from one trial to the next, subjects nevertheless used sensorimotor memories from recent movements to predict and compensate upcoming loads. Prediction enabled subjects to adapt performance so that the task was accomplished with minimum effort. Population analyses of functional images revealed a distributed, bilateral network of cortical and subcortical activity supporting predictive load compensation during visual target capture. Cortical regions – including prefrontal, parietal and hippocampal cortices – exhibited trial-by-trial fluctuations in BOLD signal consistent with the storage and recall of sensorimotor memories or “states” important for spatial working memory. Bilateral activations in associative regions of the striatum demonstrated temporal correlation with the magnitude of kinematic performance error (a signal that could drive reward-optimizing reinforcement learning and the prospective scaling of previously learned motor programs). BOLD signal correlations with load prediction were observed in the cerebellar cortex and red nuclei (consistent with the idea that these structures generate adaptive fusimotor signals facilitating cancelation of expected proprioceptive feedback, as required for conditional feedback adjustments to ongoing motor commands and feedback error learning). Analysis of single subject images revealed that predictive activity was at least as likely to be observed in more than one of these neural systems as in just one. We conclude therefore that motor adaptation is mediated by predictive compensations supported by multiple, distributed, cortical and subcortical structures
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