5,870 research outputs found
Langevin dynamics in crossed magnetic and electric fields: Hall and diamagnetic fluctuations
Based on the classical Langevin equation, we have re-visited the problem of
orbital motion of a charged particle in two dimensions for a normal magnetic
field crossed with or without an in-plane electric bias. We are led to two
interesting fluctuation effects: First, we obtain not only a longitudinal
"work-fluctuation" relation as expected for a barotropic type system, but also
a transverse work-fluctuation relation perpendicular to the electric bias. This
"Hall fluctuation" involves the product of the electric and the magnetic
fields. And second, for the case of harmonic confinement without bias, the
calculated probability density for the orbital magnetic moment gives non-zero
even moments, not derivable as field derivatives of the classical free energy.Comment: 4 pages, 2 figures, revised versio
Three-electron anisotropic quantum dots in variable magnetic fields: exact results for excitation spectra, spin structures, and entanglement
Exact-diagonalization calculations for N=3 electrons in anisotropic quantum
dots, covering a broad range of confinement anisotropies and strength of
inter-electron repulsion, are presented for zero and low magnetic fields. The
excitation spectra are analyzed as a function of the strength of the magnetic
field and for increasing quantum-dot anisotropy. Analysis of the intrinsic
structure of the many-body wave functions through spin-resolved two-point
correlations reveals that the electrons tend to localize forming Wigner
molecules. For certain ranges of dot parameters (mainly at strong anisotropy),
the Wigner molecules acquire a linear geometry, and the associated wave
functions with a spin projection S_z=1/2 are similar to the representative
class of strongly entangled states referred to as W-states. For other ranges of
parameters (mainly at intermediate anisotropy), the Wigner molecules exhibit a
more complex structure consisting of two mirror isosceles triangles. This
latter structure can be viewed as an embryonic unit of a zig-zag Wigner crystal
in quantum wires. The degree of entanglement in three-electron quantum dots can
be quantified through the use of the von Neumann entropy.Comment: To appear in Physical Review B. REVTEX4. 13 pages with 16 color
figures. To download a copy with higher-quality figures, go to publication
#78 in http://www.prism.gatech.edu/~ph274cy
Inversion improves the recognition of facial expression in thatcherized images
The Thatcher illusion provides a compelling example of the face inversion effect. However, the marked effect of inversion in the Thatcher illusion contrasts to other studies that report only a small effect of inversion on the recognition of facial expressions. To address this discrepancy, we compared the effects of inversion and thatcherization on the recognition of facial expressions. We found that inversion of normal faces caused only a small reduction in the recognition of facial expressions. In contrast, local inversion of facial features in upright thatcherized faces resulted in a much larger reduction in the recognition of facial expressions. Paradoxically, inversion of thatcherized faces caused a relative increase in the recognition of facial expressions. Together, these results suggest that different processes explain the effects of inversion on the recognition of facial expressions and on the perception of the Thatcher illusion. The grotesque perception of thatcherized images is based on a more orientation-sensitive representation of the face. In contrast, the recognition of facial expression is dependent on a more orientation-insensitive representation. A similar pattern of results was evident when only the mouth or eye region was visible. These findings demonstrate that a key component of the Thatcher illusion is to be found in orientation-specific encoding of the features of the face
Ground State Spin Oscillations of a Two-Electron Quantum Dot in a Magnetic Field
Crossings between spin-singlet and spin-triplet lowest states are analyzed
within the model of a two-electron quantum dot in a perpendicular magnetic
field. The explicit expressions in terms of the magnetic field, the magnetic
quantum number of the state and the dimensionless dot size for these
crossings are found.Comment: 8 pages, 2 figures (PS files). The paper will appear in Journal of
Physics: Condensed Matter, volume 11, issue 11 (cover date 22 March 1999) on
pages 83 - 8
Are Women’s Mate Preferences for Altruism Also Influenced by Physical Attractiveness?
Altruism plays a role in mate choice, particularly in women’s preferences, and particularly for long-term relationships. The current study analyzed how these preferences interacted with another important mate choice variable, physical attractiveness. Here, female participants were presented with photographs of men of varying levels of physical attractiveness, alongside descriptions of them behaving either altruistically or not in different scenarios. The results showed women preferred altruistic men, particularly in long-term relationships, and that this interacted with physical attractiveness such that being both attractive and altruistic made a man more desirable than just the sum of the two desirable parts. Also, being altruistic made low attractive men more desirable, but only for long-term relationships. Finally, men who were just altruistic were rated more desirable than men who were just attractive, especially for long-term relationships. Overall these findings are discussed in terms of the role of altruism in mate choice, particularly in long-term relationships and directions of future research
Emotional Strategies as Catalysts for Cooperation in Signed Networks
The evolution of unconditional cooperation is one of the fundamental problems
in science. A new solution is proposed to solve this puzzle. We treat this
issue with an evolutionary model in which agents play the Prisoner's Dilemma on
signed networks. The topology is allowed to co-evolve with relational signs as
well as with agent strategies. We introduce a strategy that is conditional on
the emotional content embedded in network signs. We show that this strategy
acts as a catalyst and creates favorable conditions for the spread of
unconditional cooperation. In line with the literature, we found evidence that
the evolution of cooperation most likely occurs in networks with relatively
high chances of rewiring and with low likelihood of strategy adoption. While a
low likelihood of rewiring enhances cooperation, a very high likelihood seems
to limit its diffusion. Furthermore, unlike in non-signed networks, cooperation
becomes more prevalent in denser topologies.Comment: 24 pages, Accepted for publication in Advances in Complex System
Integrating Species Traits into Species Pools
Despite decades of research on the species‐pool concept and the recent explosion of interest in trait‐based frameworks in ecology and biogeography, surprisingly little is known about how spatial and temporal changes in species‐pool functional diversity (SPFD) influence biodiversity and the processes underlying community assembly. Current trait‐based frameworks focus primarily on community assembly from a static regional species pool, without considering how spatial or temporal variation in SPFD alters the relative importance of deterministic and stochastic assembly processes. Likewise, species‐pool concepts primarily focus on how the number of species in the species pool influences local biodiversity. However, species pools with similar richness can vary substantially in functional‐trait diversity, which can strongly influence community assembly and biodiversity responses to environmental change. Here, we integrate recent advances in community ecology, trait‐based ecology, and biogeography to provide a more comprehensive framework that explicitly considers how variation in SPFD, among regions and within regions through time, influences the relative importance of community assembly processes and patterns of biodiversity. First, we provide a brief overview of the primary ecological and evolutionary processes that create differences in SPFD among regions and within regions through time. We then illustrate how SPFD may influence fundamental processes of local community assembly (dispersal, ecological drift, niche selection). Higher SPFD may increase the relative importance of deterministic community assembly when greater functional diversity in the species pool increases niche selection across environmental gradients. In contrast, lower SPFD may increase the relative importance of stochastic community assembly when high functional redundancy in the species pool increases the influence of dispersal history or ecological drift. Next, we outline experimental and observational approaches for testing the influence of SPFD on assembly processes and biodiversity. Finally, we highlight applications of this framework for restoration and conservation. This species‐pool functional diversity framework has the potential to advance our understanding of how local‐ and regional‐scale processes jointly influence patterns of biodiversity across biogeographic regions, changes in biodiversity within regions over time, and restoration outcomes and conservation efforts in ecosystems altered by environmental change
Negative differential conductance in quantum dots in theory and experiment
Experimental results for sequential transport through a lateral quantum dot
in the regime of spin blockade induced by spin dependent tunneling are compared
with theoretical results obtained by solving a master equation for independent
electrons. Orbital and spin effects in electron tunneling in the presence of a
perpendicular magnetic field are identified and discussed in terms of the
Fock-Darwin spectrum with spin. In the nonlinear regime, a regular pattern of
negative differential conductances is observed. Electrical asymmetries in
tunnel rates and capacitances must be introduced in order to account for the
experimental findings. Fast relaxation of the excited states in the quantum dot
have to be assumed, in order to explain the absence of certain structures in
the transport spectra.Comment: 4 pages, 4 figure
Polarization immunity of magnetoresistivity response under Microwave excitation
We analyze theoretically the dependence of the microwave polarization sate
and sense on the magnetoresistivity response of two-dimensional electron
systems. Linear and circular polarization have been considered with different
senses and directions. We discuss the polarization dependence of the
longitudinal magnetoresistivity and propose an explanation for the
experimentally observed polarization immunity, i.e., resistivity oscillations
and zero resistance state regions are unaffected by the sense of circular
polarization or by the direction of microwave electric field.Comment: 4 pages and 1 figur
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