Target Space Duality with Dilaton and Tachyon Field

We study the target space duality of classical two dimensional sigma models. The models with dilaton and tachyon field are analyzed. As a motivating example the historical electric-magnetic duality is presented. We review the construction of the duality transformation and the integrability conditions for the nonlinear sigma models with target spaces described by general metrics and antisymmetric two-forms. We generalize the formalism for the models whose actions contain the dilaton and tachyon field. For the dilaton field case it is required that the duality is a property solely of the target manifolds, independent of the world-sheet geometry. For both cases the duality transformation is established and the integrability conditions are calculated. The set of restrictions on geometrical data describing the models is obtained, the previously calculated condition on connections on target spaces is maintained in both cases.</p

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code for automatic light field microscope calibration<br

Temporal network approach to unraveling collective neuron firings

As interest escalates in the area of temporal networks, the possibility arises that such tools might help unravel the complex dynamics of potentially correlated spatiotemporal events in complex systems. Here, we present such an analysis for a dataset comprising neuronal spike trains from retinal ganglion cells in a salamander. The neuron firing events are detected experimentally using a flat array of extracellular electrodes at micrometre scale separations, with spikes from the ganglion cell layer then being sorted into single-unit spike trains. We develop a temporal network analysis of this ensemble of spike trains that allows us to explore potential causality between firings. We compare our results to a randomized system in order to deduce a statistical Z-score and find examples of both event amplification and inhibition. Although the application to neuron firings is of direct interest for understanding brain function, the network approach that we present can in principle be applied to any set of timelines detailing the occurrence of events in particular regions, sectors or entities, including the search for causality between events in human activities such as crime

Computational modeling of collective human behavior: Example of financial markets

We discuss how minimal financial market models can be constructed by bridging the gap between two existing, but incomplete, market models: a model in which a population of virtual traders make decisions based on common global information but lack local information from their social network, and a model in which the traders form a dynamically evolving social network but lack any decision-making based on global information. We show that a suitable combination of these two models -- in particular, a population of virtual traders with access to both global and local information -- produces results for the price return distribution which are closer to the reported stylized facts. We believe that this type of model can be applied across a wide range of systems in which collective human activity is observed.

Matrix metalloproteinases regulate the formation of dendritic spine head protrusions during chemically induced long-term potentiation.

Dendritic spines are are small membranous protrusions that extend from neuronal dendrites and harbor the majority of excitatory synapses. Increasing evidence has shown that matrix metalloproteinases (MMPs), a family of extracellularly acting and Zn(2+)-dependent endopeptidases, are able to rapidly modulate dendritic spine morphology. Spine head protrusions (SHPs) are filopodia-like processes that extend from the dendritic spine head, representing a form of postsynaptic structural remodeling in response to altered neuronal activity. Herein, we show that chemically induced long-term potentiation (cLTP) in dissociated hippocampal cultures upregulates MMP-9 activity that controls the formation of SHPs. Blocking of MMPs activity or microtubule dynamics abolishes the emergence of SHPs. In addition, autoactive recombinant MMP-9, promotes the formation of SHPs in organotypic hippocampal slices. Furthermore, spines with SHPs gained postsynaptic α-amino-3-hydroxyl-5-methyl-4-isoxazole propionic acid (AMPA) receptors upon cLTP and the synaptic delivery of AMPA receptors was controlled by MMPs. The present results strongly imply that MMP-9 is functionally involved in the formation of SHPs and the control of postsynaptic receptor distribution upon cLTP