Beam-Steering Nanophotonic Phased-Array Neural Probes

We demonstrate the first implantable nanophotonic neural probes with integrated silicon nitride phased arrays. Coherent beam-steering is achieved in brain tissue by wavelength tuning. Beam profiles, optogenetic stimulation, and functional imaging are validated in vitro

Cluster tendency assessment in neuronal spike data.

Sorting spikes from extracellular recording into clusters associated with distinct single units (putative neurons) is a fundamental step in analyzing neuronal populations. Such spike sorting is intrinsically unsupervised, as the number of neurons are not known a priori. Therefor, any spike sorting is an unsupervised learning problem that requires either of the two approaches: specification of a fixed value k for the number of clusters to seek, or generation of candidate partitions for several possible values of c, followed by selection of a best candidate based on various post-clustering validation criteria. In this paper, we investigate the first approach and evaluate the utility of several methods for providing lower dimensional visualization of the cluster structure and on subsequent spike clustering. We also introduce a visualization technique called improved visual assessment of cluster tendency (iVAT) to estimate possible cluster structures in data without the need for dimensionality reduction. Experimental results are conducted on two datasets with ground truth labels. In data with a relatively small number of clusters, iVAT is beneficial in estimating the number of clusters to inform the initialization of clustering algorithms. With larger numbers of clusters, iVAT gives a useful estimate of the coarse cluster structure but sometimes fails to indicate the presumptive number of clusters. We show that noise associated with recording extracellular neuronal potentials can disrupt computational clustering schemes, highlighting the benefit of probabilistic clustering models. Our results show that t-Distributed Stochastic Neighbor Embedding (t-SNE) provides representations of the data that yield more accurate visualization of potential cluster structure to inform the clustering stage. Moreover, The clusters obtained using t-SNE features were more reliable than the clusters obtained using the other methods, which indicates that t-SNE can potentially be used for both visualization and to extract features to be used by any clustering algorithm

Aerodynamics of a low-pressure turbine airfoil at low reynolds numbers-part ii: Blade-wake interaction

Part II of this two-part paper presents the aerodynamic behavior of a low-pressure high-lift turbine airfoil, PakB, under the influence of incoming wakes. The periodic unsteady effects of wakes from a single upstream blade-row were measured in a low-speed linear cascade facility at Reynolds numbers of 25,000, 50,000 and 100,000 and at two freestream turbulence intensity levels of 0.4% and 4%. In addition, eight reduced frequencies between 0.53 and 3.2, at three flow coefficients of 0.5, 0.7 and 1.0 were examined. The complex wake-induced transition, flow separation and reattachment on the suction surface boundary layer were determined from an array of closely-spaced surface hot-film sensors. The wake-induced transition caused the separated boundary layer to reattach to the suction surface at all conditions examined. The time-varying profile losses, measured downstream of the cascade, increased with decreasing Reynolds number. The influence of increased freestream turbulence intensity was only evident in between wake-passing events at low reduced frequencies. At higher values of reduced frequency, the losses increased slightly and, for the cases examined here, losses were slightly larger at lower flow coefficients. An optimum wake-passing frequency was observed at which the profile losses were a minimum

The Aerodynamics of a Low-Pressure Turbine Airfoil under Periodically Unsteady Conditions

Peer reviewed: YesNRC publication: Ye

Effect of Biofertilizers on the Yield and Yield Components of Black Cumin (Nigella sativa L.)

Abstract\ud Application of biological fertilizers is one of the most important methods for plant nutrition in ecological agriculture. In order to investigate the effect of biofertilizers on yield and yield components of black cumin (Nigella sativa L.), a field experiment was arranged in a randomized complete block design with three replications during 2007 growing season at the Agricultural Research Station of Ferdowsi University of Mashhad. Treatments included: (A) Azotobacter paspali, (B) Azospirillum brasilense, (C) the fungus of Glomus intraradaices, C+A, C+B, A+B, A+B+C, and control without no biofertilizers. In all treatments except control, the amounts of 15 mg of each biofertilizer were applied to 110 g of seeds. Results indicated that application of biofertilizers enhanced yield and yield components and decreased percentage of hollow capsules. Plant performance was better with application of Azospirillum plus mycorrhiza and a mixture of Azotobacter, Azospirillum and mycorrhiza in terms of yield determining criteria. The maximum and minimum amounts of seed yield were recorded in the B+C treatment with 41.4 gm-2, and control with 24.1 gm-2, respectively. There was no significant correlation between number of capsules per plant and seed yield, but the positive and significant correlation between number of branches per plant, number of seeds per capsule, 1000-seed weight and seed yield was observed. This study showed that application of suitable biofertilizers could increase yield and yield components of black cumin.\ud \ud Keywords: Biofertilizer, Ecological agriculture, Medicinal plants, Plant growth promoting rhizobacteri

The Influence of Reynolds Number, Turbulence Intensity and Length Scale on Separated-Flow Transition of a Low-Pressure Turbine Airfoil

Peer reviewed: YesNRC publication: Ye

Measurement and Computation of Flowfield in Transonic Turbine Nozzle Blading With Blunt Trailing Edges

Experimental and computational results are presented from cascade testing on the nozzle blading of a high pressure ratio single stage turbine. Testing on this blading in 1986 showed surprising evidence of a redistribution of the downstream total temperature field. The nozzle midspan section has subsequently been tested in a large scale low aspect ratio planar cascade, having a continuous room-temperature inlet flow, to obtain more detailed information over the subsonic and transonic speed ranges. The blades had a blunt trailing edge which caused strong von Ka\u301rma\u301n vortex shedding throughout the subsonic range. This was shown to result in Eckert-Weise effect temperature redistribution. The first time-resolved measurements of this effect were measured in this cascade. Unusual vortex configurations were also observed at transonic speeds. The purpose of the current observations was to obtain reliable time-averaged measurements of flow through the cascade, which is proving to be an excellent vehicle for validating CFD predictions. A three-hole finger probe was traversed at the inlet and outlet of the cascade to evaluate the aerodynamic performance. Mach number and base pressure distributions, together with schlieren and surface oil-flow visualization, aided understanding of flow and loss behavior. Two-dimensional numerical simulations were performed over the speed range. The results assisted understanding of the influence of Mach number on losses and flow structures, specifically the shock configurations and base pressures. Comparisons of numerical results and experimental measurements of the flow-field showed good agreement.Peer reviewed: YesNRC publication: Ye

An Experimental Investigation of Vortex-Shedding Characteristics in a Cascade of Transonic Turbine Vanes.

Peer reviewed: YesNRC publication: Ye