234 research outputs found
Inversely Unstable Solutions of Two-Dimensional Systems on Genus-p Surfaces and the Topology of Knotted Attractors
In this paper, we will show that a periodic nonlinear, time-varying
dissipative system that is defined on a genus-p surface contains one or more
invariant sets which act as attractors. Moreover, we shall generalize a result
in [Martins, 2004] and give conditions under which these invariant sets are not
homeomorphic to a circle individually, which implies the existence of chaotic
behaviour. This is achieved by studying the appearance of inversely unstable
solutions within each invariant set.Comment: 19 pages with 20 figures, AMS La-TeX, to be published in
International Journal of Bifurcation and Chao
Exploring complex networks via topological embedding on surfaces
We demonstrate that graphs embedded on surfaces are a powerful and practical
tool to generate, characterize and simulate networks with a broad range of
properties. Remarkably, the study of topologically embedded graphs is
non-restrictive because any network can be embedded on a surface with
sufficiently high genus. The local properties of the network are affected by
the surface genus which, for example, produces significant changes in the
degree distribution and in the clustering coefficient. The global properties of
the graph are also strongly affected by the surface genus which is constraining
the degree of interwoveness, changing the scaling properties from
large-world-kind (small genus) to small- and ultra-small-world-kind (large
genus). Two elementary moves allow the exploration of all networks embeddable
on a given surface and naturally introduce a tool to develop a statistical
mechanics description. Within such a framework, we study the properties of
topologically-embedded graphs at high and low `temperatures' observing the
formation of increasingly regular structures by cooling the system. We show
that the cooling dynamics is strongly affected by the surface genus with the
manifestation of a glassy-like freezing transitions occurring when the amount
of topological disorder is low.Comment: 18 pages, 7 figure
At risk of being risky: The relationship between "brain age" under emotional states and risk preference.
Developmental differences regarding decision making are often reported in the absence of emotional stimuli and without context, failing to explain why some individuals are more likely to have a greater inclination toward risk. The current study (N=212; 10-25y) examined the influence of emotional context on underlying functional brain connectivity over development and its impact on risk preference. Using functional imaging data in a neutral brain-state we first identify the "brain age" of a given individual then validate it with an independent measure of cortical thickness. We then show, on average, that "brain age" across the group during the teen years has the propensity to look younger in emotional contexts. Further, we show this phenotype (i.e. a younger brain age in emotional contexts) relates to a group mean difference in risk perception - a pattern exemplified greatest in young-adults (ages 18-21). The results are suggestive of a specified functional brain phenotype that relates to being at "risk to be risky.
Precision atomic gravimeter based on Bragg diffraction
We present a precision gravimeter based on coherent Bragg diffraction of
freely falling cold atoms. Traditionally, atomic gravimeters have used
stimulated Raman transitions to separate clouds in momentum space by driving
transitions between two internal atomic states. Bragg interferometers utilize
only a single internal state, and can therefore be less susceptible to
environmental perturbations. Here we show that atoms extracted from a
magneto-optical trap using an accelerating optical lattice are a suitable
source for a Bragg atom interferometer, allowing efficient beamsplitting and
subsequent separation of momentum states for detection. Despite the inherently
multi-state nature of atom diffraction, we are able to build a Mach-Zehnder
interferometer using Bragg scattering which achieves a sensitivity to the
gravitational acceleration of with an
integration time of 1000s. The device can also be converted to a gravity
gradiometer by a simple modification of the light pulse sequence.Comment: 13 pages, 11 figure
Law and Neuroscience: Recommendations Submitted to the President\u27s Bioethics Commission
President Obama charged the Presidential Commission for the Study of Bioethical Issues to identify a set of core ethical standards in the neuroscience domain, including the appropriate use of neuroscience in the criminal-justice system. The Commission, in turn, called for comments and recommendations. The MacArthur Foundation Research Network on Law and Neuroscience submitted a consensus statement, published here, containing 16 specific recommendations. These are organized within three main themes: 1) what steps should be taken to enhance the capacity of the criminal justice system to make sound decisions regarding the admissibility and weight of neuroscientific evidence?; 2) to what extent can the capacity of neurotechnologies to aid in the administration of criminal justice be enhanced through research?; and 3) in what additional ways might important ethical issues at the intersection of neuroscience and criminal justice be addressed
Law and Neuroscience: Recommendations Submitted to the President\u27s Bioethics Commission
President Obama charged the Presidential Commission for the Study of Bioethical Issues to identify a set of core ethical standards in the neuroscience domain, including the appropriate use of neuroscience in the criminal-justice system. The Commission, in turn, called for comments and recommendations. The MacArthur Foundation Research Network on Law and Neuroscience submitted a consensus statement, published here, containing 16 specific recommendations. These are organized within three main themes: 1) what steps should be taken to enhance the capacity of the criminal justice system to make sound decisions regarding the admissibility and weight of neuroscientific evidence?; 2) to what extent can the capacity of neurotechnologies to aid in the administration of criminal justice be enhanced through research?; and 3) in what additional ways might important ethical issues at the intersection of neuroscience and criminal justice be addressed
G2i Knowledge Brief: A Knowledge Brief of the MacArthur Foundation Research Network on Law and Neuroscience
Courts are daily confronted with admissibility issues – such as in cases involving neuroscientific testimony – that sometimes involve both the existence of a general phenomenon (i.e., “G”) and the question of whether a particular case represents a specific instance of that general phenomenon (i.e., “i”).
Unfortunately, courts have yet to carefully consider the implications of “G2i” for their admissibility decisions. In some areas, courts limit an expert’s testimony to the general phenomenon. They insist that whether the case at hand is an instance of that phenomenon is exclusively a jury question, and thus not an appropriate subject of expert opinion. In other cases, in contrast, courts hold that expert evidence must be provided on both the group-data issue (i.e., that the phenomenon exists) and what is called the “diagnostic” issue (i.e., that this case is an instance of that phenomenon).
Consequently, the MacArthur Foundation Research Network on Law and Neuroscience has prepared this knowledge brief to help courts manage the G2i divide. Specifically, we recommend that courts first determine whether proffered expert testimony concerns only the existence of the general phenomenon or instead concerns both that and the diagnosis that a particular case represents an instance of that phenomenon. Only after making that determination should the court make its admissibility decision (guided, for instance, by the Daubert factors for admitting scientific evidence)
β-Adrenoceptor blockade modulates fusiform gyrus activity to black versus white faces.
INTRODUCTION: The beta-adrenoceptor antagonist propranolol is known to reduce peripheral and central activity of noradrenaline. A recent study found that intervention with propranolol diminished negative implicit racial bias. MATERIALS AND METHOD: The current study used functional magnetic resonance imaging (fMRI) in order to determine the neural correlates of this effect. Healthy volunteers (N = 40) of white ethnic origin received a single oral dose (40 mg) of propranolol, in a randomised, double-blind, parallel group, placebo-controlled design, before viewing unfamiliar faces of same and other race. RESULTS AND DISCUSSION: We found significantly reduced activity in the fusiform gyrus and thalamus following propranolol to out-group faces only. Additionally, propranolol lowered the implicit attitude score, without affecting explicit prejudice measure. CONCLUSION: These findings suggest that noradrenaline pathways might modulate racial bias by acting on the processing of categorisation in the fusiform gyrus
The Cortisol Response to Anticipated Intergroup Interactions Predicts Self-Reported Prejudice
Objectives: While prejudice has often been shown to be rooted in experiences of threat, the biological underpinnings of this threat–prejudice association have received less research attention. The present experiment aims to test whether activations of the hypothalamus-pituitary-adrenal (HPA) axis, due to anticipated interactions with out-group members, predict self-reported prejudice. Moreover, we explore potential moderators of this relationship (i.e., interpersonal similarity; subtle vs. blatant prejudice). Methodology/Principal findings: Participants anticipated an interaction with an out-group member who was similar or dissimilar to the self. To index HPA activation, cortisol responses to this event were measured. Then, subtle and blatant prejudices were measured via questionnaires. Findings indicated that only when people anticipated an interaction with an out-group member who was dissimilar to the self, their cortisol response to this event significantly predicted subtle (r =.50) and blatant (r =.53) prejudice. Conclusions: These findings indicate that prejudicial attitudes are linked to HPA-axis activity. Furthermore, when intergroup interactions are interpreted to be about individuals (and not so much about groups), experienced threat (or its biological substrate) is less likely to relate to prejudice. This conclusion is discussed in terms of recent insights from social neuroscience
- …