Synthesis of neural networks for spatio-temporal spike pattern recognition and processing

The advent of large scale neural computational platforms has highlighted the lack of algorithms for synthesis of neural structures to perform predefined cognitive tasks. The Neural Engineering Framework offers one such synthesis, but it is most effective for a spike rate representation of neural information, and it requires a large number of neurons to implement simple functions. We describe a neural network synthesis method that generates synaptic connectivity for neurons which process time-encoded neural signals, and which makes very sparse use of neurons. The method allows the user to specify, arbitrarily, neuronal characteristics such as axonal and dendritic delays, and synaptic transfer functions, and then solves for the optimal input-output relationship using computed dendritic weights. The method may be used for batch or online learning and has an extremely fast optimization process. We demonstrate its use in generating a network to recognize speech which is sparsely encoded as spike times.Comment: In submission to Frontiers in Neuromorphic Engineerin

Neutron-Unbound Excited States of 23N

Neutron unbound states in 23N were populated via proton knockout from an 83.4 MeV/nucleon 24O beam on a liquid deuterium target. The two-body decay energy displays two peaks at E1∼100keV and E2∼1MeV with respect to the neutron separation energy. The data are consistent with shell model calculations predicting resonances at excitation energies of ∼3.6MeV and ∼4.5MeV. The selectivity of the reaction implies that these states correspond to the first and second 3/2− states. The energy of the first state is about 1.3 MeV lower than the first excited 2+ in 24O. This decrease is largely due to coupling with the πp−13/2 hole along with a small reduction of the N=16 shell gap in 23N

Reduced quasifission competition in fusion reactions forming neutron-rich heavy elements

Measurements of mass-angle distributions (MADs) for Cr + W reactions, providing a wide range in the neutron-to-proton ratio of the compound system, (N/Z)CN, have allowed for the dependence of quasifission on the (N/Z)CN to be determined in a model-independent way. Previous experimental and theoretical studies had produced conflicting conclusions. The experimental MADs reveal an increase in contact time and mass evolution of the quasifission fragments with increasing (N/Z)CN, which is indicative of an increase in the fusion probability. The experimental results are in agreement with microscopic time-dependent Hartree-Fock calculations of the quasifission process. The experimental and theoretical results favor the use of the most neutron-rich projectiles and targets for the production of heavy and superheavy nuclei.Comment: Accepted to PRC as a Rapid Communicatio

Two-Neutron Sequential Decay of 24^{24}O

A two-neutron unbound excited state of $^{24}$O was populated through a (d,d') reaction at 83.4 MeV/nucleon. A state at $E = 715 \pm 110$ (stat) $\pm 45$ (sys) keV with a width of $\Gamma < 2$ MeV was observed above the two-neutron separation energy placing it at 7.65 $\pm$ 0.2 MeV with respect to the ground state. Three-body correlations for the decay of $^{24}$O $\rightarrow$ $^{22}$O + $2n$ show clear evidence for a sequential decay through an intermediate state in $^{23}$O. Neither a di-neutron nor phase-space model for the three-body breakup were able to describe these correlations

Duality properties of Gorringe-Leach equations

In the category of motions preserving the angular momentum's direction, Gorringe and Leach exhibited two classes of differential equations having elliptical orbits. After enlarging slightly these classes, we show that they are related by a duality correspondence of the Arnold-Vassiliev type. The specific associated conserved quantities (Laplace-Runge-Lenz vector and Fradkin-Jauch-Hill tensor) are then dual reflections one of the othe

Tb3+-doped LaF3 nanocrystals for correlative cathodoluminescence electron microscopy imaging with nanometric resolution in focused ion beam-sectioned biological samples

Here, we report the use of rare earth element-doped nanocrystals as probes for correlative cathodoluminescence electron microscopy (CCLEM) bioimaging. This first experimental demonstration shows potential for the simultaneous acquisition of luminescence and electron microscopy images with nanometric resolution in focused ion beam cut biological samples

X-ray absorption spectroscopy systematics at the tungsten L-edge

A series of mononuclear six-coordinate tungsten compounds spanning formal oxidation states from 0 to +VI, largely in a ligand environment of inert chloride and/or phosphine, has been interrogated by tungsten L-edge X-ray absorption spectroscopy. The L-edge spectra of this compound set, comprised of [W&lt;sup&gt;0&lt;/sup&gt;(PMe&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;6&lt;/sub&gt;], [W&lt;sup&gt;II&lt;/sup&gt;Cl&lt;sub&gt;2&lt;/sub&gt;(PMePh&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;4&lt;/sub&gt;], [W&lt;sup&gt;III&lt;/sup&gt;Cl&lt;sub&gt;2&lt;/sub&gt;(dppe)&lt;sub&gt;2&lt;/sub&gt;][PF&lt;sub&gt;6&lt;/sub&gt;] (dppe = 1,2-bis(diphenylphosphino)ethane), [W&lt;sup&gt;IV&lt;/sup&gt;Cl&lt;sub&gt;4&lt;/sub&gt;(PMePh&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;], [W&lt;sup&gt;V&lt;/sup&gt;(NPh)Cl&lt;sub&gt;3&lt;/sub&gt;(PMe&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;], and [W&lt;sup&gt;VI&lt;/sup&gt;Cl&lt;sub&gt;6&lt;/sub&gt;] correlate with formal oxidation state and have usefulness as references for the interpretation of the L-edge spectra of tungsten compounds with redox-active ligands and ambiguous electronic structure descriptions. The utility of these spectra arises from the combined correlation of the estimated branching ratio (EBR) of the L&lt;sub&gt;3,2&lt;/sub&gt;-edges and the L&lt;sub&gt;1&lt;/sub&gt; rising-edge energy with metal Z&lt;sub&gt;eff&lt;/sub&gt;, thereby permitting an assessment of effective metal oxidation state. An application of these reference spectra is illustrated by their use as backdrop for the L-edge X-ray absorption spectra of [W&lt;sup&gt;IV&lt;/sup&gt;(mdt)&lt;sub&gt;2&lt;/sub&gt;(CO)&lt;sub&gt;2&lt;/sub&gt;] and [W&lt;sup&gt;IV&lt;/sup&gt;(mdt)&lt;sub&gt;2&lt;/sub&gt;(CN)&lt;sub&gt;2&lt;/sub&gt;]&lt;sup&gt;2–&lt;/sup&gt; (mdt&lt;sup&gt;2–&lt;/sup&gt; = 1,2-dimethylethene-1,2-dithiolate), which shows that both compounds are effectively W&lt;sup&gt;IV&lt;/sup&gt; species. Use of metal L-edge XAS to assess a compound of uncertain formulation requires: 1) Placement of that data within the context of spectra offered by unambiguous calibrant compounds, preferably with the same coordination number and similar metal ligand distances. Such spectra assist in defining upper and/or lower limits for metal Z&lt;sub&gt;eff&lt;/sub&gt; in the species of interest; 2) Evaluation of that data in conjunction with information from other physical methods, especially ligand K-edge XAS; 3) Increased care in interpretation if strong π-acceptor ligands, particularly CO, or π-donor ligands are present. The electron-withdrawing/donating nature of these ligand types, combined with relatively short metal-ligand distances, exaggerate the difference between formal oxidation state and metal Z&lt;sub&gt;eff&lt;/sub&gt; or, as in the case of [W&lt;sup&gt;IV&lt;/sup&gt;(mdt)&lt;sub&gt;2&lt;/sub&gt;(CO)&lt;sub&gt;2&lt;/sub&gt;], add other subtlety by modulating the redox level of other ligands in the coordination sphere