1,322 research outputs found
Quantitative genetic versions of Hamilton's rule with empirical applications
Hamilton's theory of inclusive fitness revolutionized our understanding of the evolution of social interactions. Surprisingly, an incorporation of Hamilton's perspective into the quantitative genetic theory of phenotypic evolution has been slow, despite the popularity of quantitative genetics in evolutionary studies. Here, we discuss several versions of Hamilton's rule for social evolution from a quantitative genetic perspective, emphasizing its utility in empirical applications. Although evolutionary quantitative genetics offers methods to measure each of the critical parameters of Hamilton's rule, empirical work has lagged behind theory. In particular, we lack studies of selection on altruistic traits in the wild. Fitness costs and benefits of altruism can be estimated using a simple extension of phenotypic selection analysis that incorporates the traits of social interactants. We also discuss the importance of considering the genetic influence of the social environment, or indirect genetic effects (IGEs), in the context of Hamilton's rule. Research in social evolution has generated an extensive body of empirical work focusing—with good reason—almost solely on relatedness. We argue that quantifying the roles of social and non-social components of selection and IGEs, in addition to relatedness, is now timely and should provide unique additional insights into social evolution
Novel RNA modifications in the nervous system: form and function
Modified RNA molecules have recently been shown to regulate nervous system functions. This mini-review and associated mini-symposium provide an overview of the types and known functions of novel modified RNAs in the nervous system, including covalently modified RNAs, edited RNAs, and circular RNAs. We discuss basic molecular mechanisms involving RNA modifications as well as the impact of modified RNAs and their regulation on neuronal processes and disorders, including neural fate specification, intellectual disability, neurodegeneration, dopamine neuron function, and substance use disorders
Segregation of granular binary mixtures by a ratchet mechanism
We report on a segregation scheme for granular binary mixtures, where the
segregation is performed by a ratchet mechanism realized by a vertically shaken
asymmetric sawtooth-shaped base in a quasi-two-dimensional box. We have studied
this system by computer simulations and found that most binary mixtures can be
segregated using an appropriately chosen ratchet, even when the particles in
the two components have the same size, and differ only in their normal
restitution coefficient or friction coefficient. These results suggest that the
components of otherwise non-segregating granular mixtures may be separated
using our method.Comment: revtex, 4 pages, 4 figures, submitte
A Deformation of Twistor Space and a Chiral Mass Term in N=4 Super Yang-Mills Theory
Super twistor space admits a certain (super) complex structure deformation
that preserves the Poincare subgroup of the symmetry group PSL(4|4) and depends
on 10 parameters. In a previous paper [hep-th/0502076], it was proposed that in
twistor string theory this deformation corresponds to augmenting N=4 super
Yang-Mills theory by a mass term for the left-chirality spinors. In this paper
we analyze this proposal in more detail. We calculate 4-particle scattering
amplitudes of fermions, gluons and scalars and show that they are supported on
holomorphic curves in the deformed twistor space.Comment: 52 pages, 15 figure
Understanding Terrorist Organizations with a Dynamic Model
Terrorist organizations change over time because of processes such as
recruitment and training as well as counter-terrorism (CT) measures, but the
effects of these processes are typically studied qualitatively and in
separation from each other. Seeking a more quantitative and integrated
understanding, we constructed a simple dynamic model where equations describe
how these processes change an organization's membership. Analysis of the model
yields a number of intuitive as well as novel findings. Most importantly it
becomes possible to predict whether counter-terrorism measures would be
sufficient to defeat the organization. Furthermore, we can prove in general
that an organization would collapse if its strength and its pool of foot
soldiers decline simultaneously. In contrast, a simultaneous decline in its
strength and its pool of leaders is often insufficient and short-termed. These
results and other like them demonstrate the great potential of dynamic models
for informing terrorism scholarship and counter-terrorism policy making.Comment: To appear as Springer Lecture Notes in Computer Science v2:
vectorized 4 figures, fixed two typos, more detailed bibliograph
Spin splitting and precession in quantum dots with spin-orbit coupling: the role of spatial deformation
Extending a previous work on spin precession in GaAs/AlGaAs quantum dots with
spin-orbit coupling, we study the role of deformation in the external
confinement. Small elliptical deformations are enough to alter the precessional
characteristics at low magnetic fields. We obtain approximate expressions for
the modified factor including weak Rashba and Dresselhaus spin-orbit terms.
For more intense couplings numerical calculations are performed. We also study
the influence of the magnetic field orientation on the spin splitting and the
related anisotropy of the factor. Using realistic spin-orbit strengths our
model calculations can reproduce the experimental spin-splittings reported by
Hanson et al. (cond-mat/0303139) for a one-electron dot. For dots containing
more electrons, Coulomb interaction effects are estimated within the
local-spin-density approximation, showing that many features of the
non-iteracting system are qualitatively preserved.Comment: 7 pages, 7 figure
F-spin as a Partial Symmetry
We use the empirical evidence that F-spin multiplets exist in nuclei for only
selected states as an indication that F-spin can be regarded as a partial
symmetry. We show that there is a class of non-F-scalar IBM-2 Hamiltonians with
partial F-spin symmetry, which reproduce the known systematics of collective
bands in nuclei. These Hamiltonians predict that the scissors states have good
F-spin and form F-spin multiplets, which is supported by the existing data.Comment: 14 pages, 1 figur
Anisotropic splitting of intersubband spin plasmons in quantum wells with bulk and structural inversion asymmetry
In semiconductor heterostructures, bulk and structural inversion asymmetry
and spin-orbit coupling induce a k-dependent spin splitting of valence and
conduction subbands, which can be viewed as being caused by momentum-dependent
crystal magnetic fields. This paper studies the influence of these effective
magnetic fields on the intersubband spin dynamics in an asymmetric n-type
GaAs/AlGaAs quantum well. We calculate the dispersions of intersubband spin
plasmons using linear response theory. The so-called D'yakonov-Perel'
decoherence mechanism is inactive for collective intersubband excitations,
i.e., crystal magnetic fields do not lead to decoherence of spin plasmons.
Instead, we predict that the main signature of bulk and structural inversion
asymmetry in intersubband spin dynamics is a three-fold, anisotropic splitting
of the spin plasmon dispersion. The importance of many-body effects is pointed
out, and conditions for experimental observation with inelastic light
scattering are discussed.Comment: 8 pages, 6 figure
Dissection of a composite volcanic earthquake at Santiaguito, Guatemala
Volcano earthquake sources associated with eruptions at Santiaguito volcano in Guatemala are complex. Rock fracture, fluid now, and gas expansion occur at variable time scales and induce superposed ground motions, including both static and dynamic deformation, and atmospheric pressure disturbances. Dissection of this composite event is facilitated through extra-seismic observations, such as infrasound, geodetic, and visual monitoring. Multi-parametric investigation of an eruptive event on Jan. 4th 2009 reveals increased degassing, apparent as both geodetic tilt and harmonic seismoinfrasonic tremor, preceding an explosive event. The explosive event itself entails surface dome uplift, multiple eruptive pulses, and subsequent re-equilibration of the volcanic edifice manifested in derived tilt. We report here on an integrated approach to discerning the physical processes at the actively effusing and exploding Santiaguito volcano and describe the composite earthquake that ' occurs here
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