20,083 research outputs found
For the good of the group? Exploring group-level evolutionary adaptations using multilevel selection theory.
In this paper, we present an evolutionary framework, multilevel selection theory (MLS), that is highly amenable to existing social psychological theory and empiricism. MLS provides an interpretation of natural selection that shows how group-beneficial traits can evolve, a prevalent implication of social psychological data. We outline the theory and provide a number of example topics, focusing on prosociality, policing behavior, gossip, brainstorming, distributed cognition, and social identity. We also show that individual differences can produce important group-level outcomes depending on differential aggregation of individual types and relate this to the evolutionary dynamics underlying group traits. Drawing on existing work, we show how social psychologists can integrate this framework into their research program and suggest future directions for research
On the effect of the atmosphere on the evaporation of sessile droplets of water
An experimental and theoretical study into the effect of the atmosphere on the evaporation of pinned sessile droplets of water is described. The experimental work investigated the evaporation rates of sessile droplets in atmospheres of three different ambient gases (namely, helium, nitrogen and carbon dioxide) at reduced pressure (from 40 to 1000 mbar) using four different substrates(namely, aluminium, titanium, Macor and PTFE) with a wide range of thermal conductivities.Reducing the atmospheric pressure increases the diffusion coefficient of water vapour in the atmosphere and hence increases the evaporation rate. Changing the ambient gas also alters the diffusion coefficient and hence also affects the evaporation rate. A mathematical model that takes into account the effect of the atmospheric pressure and the nature of the ambient gas on the diffusion of water vapour in the atmosphere and the thermal conductivity of the substrate is developed, and its predictions are found to be in encouraging agreement with the experimental results
Isospectral deformations of closed Riemannian manifolds with different scalar curvature
We construct the first examples of continuous families of isospectral
Riemannian metrics that are not locally isometric on closed manifolds, more
precisely, on , where is a torus of dimension and
is a sphere of dimension . These metrics are not locally
homogeneous; in particular, the scalar curvature of each metric is nonconstant.
For some of the deformations, the maximum scalar curvature changes during the
deformation.Comment: amstex, 10 pages, no figure
On the Forward-Backward Asymmetry of Leptonic Decays of at the Fermilab Tevatron
We report on a study of the measurement techniques used to determine the
leptonic forward-backward asymmetry of top anti-top quark pairs in Tevatron
experiments with a proton anti-proton initial state. Recently it was shown that
a fit of the differential asymmetry as a function of (where
is the charge of the lepton from the cascade decay of the top quarks
and is the final pseudorapidity of the lepton in the detector frame)
to a hyperbolic tangent function can be used to extrapolate to the full
leptonic asymmetry. We find this empirical method to well reproduce the results
from current experiments, and present arguments as to why this is the case. We
also introduce two more models, based on Gaussian functions, that better model
the distribution. With our better understanding, we find that
the asymmetry is mainly determined by the shift of the mean of the
distribution, the main contribution to the inclusive asymmetry
comes from the region around , and the extrapolation from
the detector-covered region to the inclusive asymmetry is stable via a
multiplicative scale factor, giving us confidence in the previously reported
experimental results.Comment: 26 pages, 12 figure
Chapter 3- How Adult Education Can Inform Optimal Online Learning
David\u27s Story
I first met Krissy Wilson in 2015 when I was asked to design a new graduate course at Northwestern University on learning environment design. Krissy was part of the talented Distance Learning team in the School of Professional Studies. I was a teacher, instructional specialist, and reluctant learning management system administrator at an arts-based city college where I had worked for almost 15 years.
Krissy\u27s Story
I got to know David Noffs first as a faculty member in the Master in Information Design and Strategy program in the School of Professional Studies at Northwestern University. Before he joined the Distance Learning team as a learning designer, he was already well-known to all of us as “power faculty,” the kind of instructor who took online course development both seriously and creatively and always showed up for professional development
Do the surface Fermi arcs in Weyl semimetals survive disorder?
We theoretically study the topological robustness of the surface physics
induced by Weyl Fermi-arc surface states in the presence of short-ranged
quenched disorder and surface-bulk hybridization. This is investigated with
numerically exact calculations on a lattice model exhibiting Weyl Fermi-arcs.
We find that the Fermi-arc surface states, in addition to having a finite
lifetime from disorder broadening, hybridize with nonperturbative bulk rare
states making them no longer bound to the surface (i.e. they lose their purely
surface spectral character). Thus, we provide strong numerical evidence that
the Weyl Fermi-arcs are not topologically protected from disorder. Nonetheless,
the surface chiral velocity is robust and survives in the presence of strong
disorder, persisting all the way to the Anderson-localized phase by forming
localized current loops that live within the localization length of the
surface. Thus, the Weyl semimetal is not topologically robust to the presence
of disorder, but the surface chiral velocity is.Comment: Single column; 24 pages, 12 figure
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