2,937 research outputs found
Supervised Associative Learning in Spiking Neural Network
In this paper, we propose a simple supervised associative learning approach for spiking neural networks. In an excitatory-inhibitory network paradigm with Izhikevich spiking neurons, synaptic plasticity is implemented on excitatory to excitatory synapses dependent on both spike emission rates and spike timings. As results of learning, the network is able to associate not just familiar stimuli but also novel stimuli observed through synchronised activity within the same subpopulation and between two associated subpopulations
Intelligent systems in the context of surrounding environment
We investigate the behavioral patterns of a population of agents, each controlled by a simple biologically motivated neural network model, when they are set in competition against each other in the Minority Model of Challet and Zhang. We explore the effects of changing agent characteristics, demonstrating that crowding behavior takes place among agents of similar memory, and show how this allows unique `rogue' agents with higher memory values to take advantage of a majority population. We also show that agents' analytic capability is largely determined by the size of the intermediary layer of neurons.
In the context of these results, we discuss the general nature of natural and artificial intelligence systems, and suggest intelligence only exists in the context of the surrounding environment (embodiment).
Source code for the programs used can be found at http://neuro.webdrake.net/
Novel designs for Penning ion traps
We present a number of alternative designs for Penning ion traps suitable for
quantum information processing (QIP) applications with atomic ions. The first
trap design is a simple array of long straight wires which allows easy optical
access. A prototype of this trap has been built to trap Ca+ and a simple
electronic detection scheme has been employed to demonstrate the operation of
the trap. Another trap design consists of a conducting plate with a hole in it
situated above a continuous conducting plane. The final trap design is based on
an array of pad electrodes. Although this trap design lacks the open geometry
of the traps described above, the pad design may prove useful in a hybrid
scheme in which information processing and qubit storage take place in
different types of trap. The behaviour of the pad traps is simulated
numerically and techniques for moving ions rapidly between traps are discussed.
Future experiments with these various designs are discussed. All of the designs
lend themselves to the construction of multiple trap arrays, as required for
scalable ion trap QIP.Comment: 11 pages, 10 figure
Relational and Overt Aggression in Preschool
This research was designed as an initial attempt to assess relational aggression in preschool-age children. Our goal was to develop reliable measures of relational aggression for young children and to use these instruments to address several important issues (e.g., the relation between this form of aggression and social–psychological adjustment). Results provide evidence that relationally aggressive behaviors appear in children\u27s behavioral repertoires at relatively young ages, and that these behaviors can be reliably distinguished from overtly aggressive behaviors in preschool-age children. Further, findings indicate that preschool girls are significantly more relationally aggressive and less overtly aggressive than preschool boys. Finally, results show that relational aggression is significantly related to social–psychological maladjustment (e.g., peer rejection) for both boys and girls
Relational and Physical Forms of Peer Victimization in Preschool
Recent studies of peer victimization have demonstrated the importance of studying relational as well as physical forms of peer maltreatment for understanding children\u27s social-psychological adjustment problems. Studies in this area have been limited thus far by a focus on school-age children (9–12-year olds). Given the significance of early identification of children\u27s social difficulties for intervention and prevention efforts, this research was designed to assess relational and physical peer victimization among preschool-age children (3–5-year-olds). Results indicated that boys were significantly more physically victimized than girls whereas girls were more relationally victimized. Both relational and physical victims experienced greater adjustment problems than did their peers. Relational victimization contributed unique information about adjustment beyond that provided by physical victimization
Toward a More Comprehensive Understanding of Peer Maltreatment: Studies of Relational Victimization
Although many past studies of peer maltreatment have focused on physical victimization, the importance of an empirical focus on relational victimization has only recently been recognized. In relational victimization, the perpetrator attempts to harm the target through the manipulation of relationships, threat of damage to them, or both. We review what is currently known about relational victimization with three issues in mind: (a) developmental changes in the manifestation of relational victimization, (b) gender differences in the likelihood of being victimized, and (c) evidence that relational victimization is harmful
Synchronized dynamics of cortical neurons with time-delay feedback
The dynamics of three mutually coupled cortical neurons with time delays in
the coupling are explored numerically and analytically. The neurons are coupled
in a line, with the middle neuron sending a somewhat stronger projection to the
outer neurons than the feedback it receives, to model for instance the relay of
a signal from primary to higher cortical areas. For a given coupling
architecture, the delays introduce correlations in the time series at the
time-scale of the delay. It was found that the middle neuron leads the outer
ones by the delay time, while the outer neurons are synchronized with zero lag
times. Synchronization is found to be highly dependent on the synaptic time
constant, with faster synapses increasing both the degree of synchronization
and the firing rate. Analysis shows that presynaptic input during the
interspike interval stabilizes the synchronous state, even for arbitrarily weak
coupling, and independent of the initial phase. The finding may be of
significance to synchronization of large groups of cells in the cortex that are
spatially distanced from each other.Comment: 21 pages, 11 figure
Robust formation of morphogen gradients
We discuss the formation of graded morphogen profiles in a cell layer by
nonlinear transport phenomena, important for patterning developing organisms.
We focus on a process termed transcytosis, where morphogen transport results
from binding of ligands to receptors on the cell surface, incorporation into
the cell and subsequent externalization. Starting from a microscopic model, we
derive effective transport equations. We show that, in contrast to morphogen
transport by extracellular diffusion, transcytosis leads to robust ligand
profiles which are insensitive to the rate of ligand production
Dynamics of axialized laser-cooled ions in a Penning trap
We report the experimental characterization of axialization - a method of
reducing the magnetron motion of a small number of ions stored in a Penning
trap. This is an important step in the investigation of the suitability of
Penning traps for quantum information processing. The magnetron motion was
coupled to the laser-cooled modified cyclotron motion by the application of a
near-resonant oscillating quadrupole potential (the "axialization drive").
Measurement of cooling rates of the radial motions of the ions showed an
order-of-magnitude increase in the damping rate of the magnetron motion with
the axialization drive applied. The experimental results are in good
qualitative agreement with a recent theoretical study. In particular, a
classical avoided crossing was observed in the motional frequencies as the
axialization drive frequency was swept through the optimum value, proving that
axialization is indeed a resonant effect.Comment: 8 pages, 9 figure
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