Optical Emissions from Ensembles of Nanoclusters with High Concentrations of Stabilized Nitrogen Atoms

Ensembles of nanoclusters are formed in bulk HeII by the injection of products of a radiofrequency discharge in impurity-helium gas mixtures into bulk superfluid ^4He (HeII). The ensembles of nanoclusters contain high concentrations of stabilized nitrogen atoms residing mostly on the surfaces of rare gas or nitrogen nanoclusters. These samples are characterized by a high energy density which allows the study of energy release processes in chemical reactions initiated by warming ensembles of nanoclusters. Optical spectra in the ultra-violet, visible, and near-infrared ranges were recorded during the destruction of these ensembles of nanoclusters, accompanied by a rapid release of chemical energy stored in the samples. Rare gases such as neon, argon, and krypton were used to study the effects of changing the relative concentrations of nitrogen in rare gases used for sample preparation on thermoluminescence spectra during destruction of nitrogen-rare gas-helium samples. Spectra obtained during the bright flashes of the final destruction of the samples contain M- and β-bands of NO molecules the intensities of which depend on concentration of molecular nitrogen in the gas mixture as well as on the type of rare gas present in the gas mixture. During the destructions of samples containing stabilized nitrogen, oxygen, hydrogen, and deuterium atoms, the known bands of atomic nitrogen and oxygen, and bands of molecular nitrogen, oxygen, and NO were observed as well as several other interesting features including a broad band near ʎ ~ 360 nm, which has been identified as an emission corresponding to the 2Avg →1Avg transition of Nv4(Dv2h) polymeric nitrogen. Also the sharp lines at ʎ = 336 nm, 473 nm, and 1170 nm were observed, which were assigned to the emission of the ND radicals formed due to recombinations of nitrogen atoms in excited metastable states and deuterium atoms in the ground state during the destruction of ensembles of molecular nitrogen nanoclusters. The influence of rotation speed of a beaker containing HeII on the intensity of luminescence of collections of nanoclusters immersed in HeII was also studied. Luminescence was found to increase with the concentration of molecular nitrogen in the nitrogen-helium gas mixtures used for the formation of the molecular nitrogen nanoclusters. The intensity of α-group emission of nitrogen atoms (^2D → ^4S transition) in nanoclusters also increased with the rotational speed of the beaker. We suggest that this effect is connected to the processes of recombination of nitrogen atoms residing on the surfaces of nanoclusters after their trapping into quantum vortices in HeII. Increasing the rotation speed of the beaker results in the increasing density of quantum vortices in HeII. The probability for nanoclusters to become trapped in the vortex cores increases with the vortex density. Inside the vortex cores, the collision rate of nanoclusters increases substantially, leading to more efficient recombination of nitrogen atoms stabilized on the surfaces of nanoclusters and, therefore to more intense atomic nitrogen luminescence

Optical Emissions from Ensembles of Nanoclusters with High Concentrations of Stabilized Nitrogen Atoms

Ensembles of nanoclusters are formed in bulk HeII by the injection of products of a radiofrequency discharge in impurity-helium gas mixtures into bulk superfluid ^4He (HeII). The ensembles of nanoclusters contain high concentrations of stabilized nitrogen atoms residing mostly on the surfaces of rare gas or nitrogen nanoclusters. These samples are characterized by a high energy density which allows the study of energy release processes in chemical reactions initiated by warming ensembles of nanoclusters. Optical spectra in the ultra-violet, visible, and near-infrared ranges were recorded during the destruction of these ensembles of nanoclusters, accompanied by a rapid release of chemical energy stored in the samples. Rare gases such as neon, argon, and krypton were used to study the effects of changing the relative concentrations of nitrogen in rare gases used for sample preparation on thermoluminescence spectra during destruction of nitrogen-rare gas-helium samples. Spectra obtained during the bright flashes of the final destruction of the samples contain M- and β-bands of NO molecules the intensities of which depend on concentration of molecular nitrogen in the gas mixture as well as on the type of rare gas present in the gas mixture. During the destructions of samples containing stabilized nitrogen, oxygen, hydrogen, and deuterium atoms, the known bands of atomic nitrogen and oxygen, and bands of molecular nitrogen, oxygen, and NO were observed as well as several other interesting features including a broad band near ʎ ~ 360 nm, which has been identified as an emission corresponding to the 2Avg →1Avg transition of Nv4(Dv2h) polymeric nitrogen. Also the sharp lines at ʎ = 336 nm, 473 nm, and 1170 nm were observed, which were assigned to the emission of the ND radicals formed due to recombinations of nitrogen atoms in excited metastable states and deuterium atoms in the ground state during the destruction of ensembles of molecular nitrogen nanoclusters. The influence of rotation speed of a beaker containing HeII on the intensity of luminescence of collections of nanoclusters immersed in HeII was also studied. Luminescence was found to increase with the concentration of molecular nitrogen in the nitrogen-helium gas mixtures used for the formation of the molecular nitrogen nanoclusters. The intensity of α-group emission of nitrogen atoms (^2D → ^4S transition) in nanoclusters also increased with the rotational speed of the beaker. We suggest that this effect is connected to the processes of recombination of nitrogen atoms residing on the surfaces of nanoclusters after their trapping into quantum vortices in HeII. Increasing the rotation speed of the beaker results in the increasing density of quantum vortices in HeII. The probability for nanoclusters to become trapped in the vortex cores increases with the vortex density. Inside the vortex cores, the collision rate of nanoclusters increases substantially, leading to more efficient recombination of nitrogen atoms stabilized on the surfaces of nanoclusters and, therefore to more intense atomic nitrogen luminescence

Community-based benchmarking improves spike rate inference from two-photon calcium imaging data

In recent years, two-photon calcium imaging has become a standard tool to probe the function of neural circuits and to study computations in neuronal populations. However, the acquired signal is only an indirect measurement of neural activity due to the comparatively slow dynamics of fluorescent calcium indicators. Different algorithms for estimating spike rates from noisy calcium measurements have been proposed in the past, but it is an open question how far performance can be improved. Here, we report the results of the spikefinder challenge, launched to catalyze the development of new spike rate inference algorithms through crowd-sourcing. We present ten of the submitted algorithms which show improved performance compared to previously evaluated methods. Interestingly, the top-performing algorithms are based on a wide range of principles from deep neural networks to generative models, yet provide highly correlated estimates of the neural activity. The competition shows that benchmark challenges can drive algorithmic developments in neuroscience

26th Annual Computational Neuroscience Meeting (CNS*2017): Part 3 - Meeting Abstracts - Antwerp, Belgium. 15–20 July 2017

This work was produced as part of the activities of FAPESP Research,\ud Disseminations and Innovation Center for Neuromathematics (grant\ud 2013/07699-0, S. Paulo Research Foundation). NLK is supported by a\ud FAPESP postdoctoral fellowship (grant 2016/03855-5). ACR is partially\ud supported by a CNPq fellowship (grant 306251/2014-0)

Properties of axonal and synaptic extracellular field potentials in the barn owl

Im Gehirn gemessene Extrazelluläre Feldpotentiale (EFPs) sind ein wichtiges Maß für neuronale Aktivität. In vielen Fällen ist der genaue physiologische Ursprung dieser Potentiale unbekannt oder umstritten. Der auditorische Hirnstamm der Schleiereule bietet eine ausgezeichnete Möglichkeit, die EFPs und ihren Ursprung zu untersuchen. Der Hirnstamm der Eule ist ideal, weil das Feldpotential in ihm sehr stark ist, weil die zugrundeliegende Anatomie wohl-untersucht ist, und weil das Potential sehr einfach durch auditorische Stimulation gesteuert werden kann. In dieser Arbeit präsentiere ich zwei Beispiele, in welchen ich mir die einzigartigen Eigenschaften der Schleiereule zunutze mache, um das EFP zu erforschen. Das erste Beispiel behandelt Axone, und ich zeige, dass neuronale Aktivität in Axonbündeln, welche eine charakteristische Endzone besitzen, ein starkes Dipolmoment erzeugen kann. Im zweiten Beispiel behandele ich Synapsen. Aus den EFPs der Synapsen konnte ich die Merkmale der synaptischen Kurzzeitplastizität extrahieren. Die Methoden und Erkenntnisse die ich entwickelt habe sind auf andere Organismen übertragbar und erweitern das Verständnis vom Einfluss unterschiedlicher anatomischer Strukturen auf das EFP.Extracellular field potentials (EFPs) recorded in the brain are an important indicator of neural activity for neuroscientists. In many cases, their physiological basis is unknown or debated. The barn owl auditory brainstem provides an excellent opportunity to study these EFPs and their origins. The barn owl auditory brainstem is ideal because the field potentials are very large and very easily controlled by the auditory stimulus, and the underlying anatomy is well known. Here I present two examples of exploiting the unique properties of the EFP in the barn owl auditory brainstem. The first is concerned with axons, where I show that activity in axon bundles with characteristic termination zones generates strong dipole moments. The second example is concerned with synaptic currents, from which I was able to extract a signature of short-term plasticity. The methods and insights I developed are applicable to other organisms as well, and contribute to the general understanding of the roles different anatomical structures can play in the generation of EFPs