This paper presents a deterministic and adaptive spike model derived from radial basis functionsand a leaky integrate-and-fire sampler developed for training spiking neural networks without directweight manipulation. ...
This paper presents a deterministic and adaptive spike model derived from radial basis functions
and a leaky integrate-and-fire sampler developed for training spiking neural networks without direct
weight manipulation. Several algorithms have been proposed for training spiking neural networks
through biologically-plausible learning mechanisms, such as spike-timing-dependent synaptic plasticity
and Hebbian plasticity. These algorithms typically rely on the ability to update the synaptic strengths,
or weights, directly, through a weight update rule in which the weight increment can be decided
and implemented based on the training equations. However, in several potential applications of
adaptive spiking neural networks, including neuroprosthetic devices and CMOS/memristor nanoscale
neuromorphic chips, the weights cannot be manipulated directly and, instead, tend to change over time
by virtue of the pre- and postsynaptic neural activity. This paper presents an indirect learning method
that induces changes in the synaptic weights by modulating spike-timing-dependent plasticity by means
of controlled input spike trains. In place of the weights, the algorithm manipulates the input spike trains
used to stimulate the input neurons by determining a sequence of spike timings that minimize a desired
objective function and, indirectly, induce the desired synaptic plasticity in the network.
It was recently discovered that in addition to its exotic electronic properties graphene reveals unusually high intrinsic thermal *** physics of phonons–the main heat carriers in graphene–was shown to be substantial...
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It was recently discovered that in addition to its exotic electronic properties graphene reveals unusually high intrinsic thermal *** physics of phonons–the main heat carriers in graphene–was shown to be substantially different in two-dimensional(2D)crystals,such as graphene,than in three-dimensional(3D)***,we report
We show evidence of electrical and thermal conductivity percolation in polymer based carbon nanotube (CNT) composites, which follow power law variations with respect to the CNT concentrations in the matrix. The experi...
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We show evidence of electrical and thermal conductivity percolation in polymer based carbon nanotube (CNT) composites, which follow power law variations with respect to the CNT concentrations in the matrix. The experimentally obtained percolation thresholds, i.e., ~ 0.074 vol % for single walled CNTs and ~ 2.0 vol % for multi-walled CNTs, were found to be aspect ratio dependent and in accordance with those determined theoretically from excluded volume percolation theory. A much greater enhancement, over 10 orders of magnitude, was obtained in the electrical conductivity at the percolation threshold, while a smaller increase of ~ 100 % was obtained in the thermal conductivity values. Such a difference is qualitatively explained on the basis of the respective conductivity contrast between the CNT filler and the polymer matrix.
Sapphire wafers are widely used as the substrates for fabricating GaN light-emitting diodes (LEDs). The quality of LEDs depends directly on the quality of the sapphire wafers. A series of machining processes is requir...
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Sapphire wafers are widely used as the substrates for fabricating GaN light-emitting diodes (LEDs). The quality of LEDs depends directly on the quality of the sapphire wafers. A series of machining processes is required to turn sapphire barstock into wafers with the desired geometry and surface quality. This paper reviews the literature on various machining processes for sapphire wafers: slicing (including outer diameter cut-off grinding, inner diameter cut-off grinding, loose abrasive multi-wire sawing, fixed abrasive slicing, and fixed abrasive multi-wire sawing), flattening (including lapping and grinding), and surface finishing (including mechanical polishing and chemical mechanical polishing). New machining technologies are also introduced.
Nanomechanical mapping of individual multi-walled carbon nanotubes (MWNTs) has been undertaken to investigate intra-tube variations of mechanical response. Ultrasonic force microscopy has been used to measure the rela...
Nanomechanical mapping of individual multi-walled carbon nanotubes (MWNTs) has been undertaken to investigate intra-tube variations of mechanical response. Ultrasonic force microscopy has been used to measure the relative axial and radial variations of contact stiffness of individual MWNTs synthesized using chemical vapor deposition (CVD) and arc-discharge (AD) techniques. For CVD-based MWNTs the contact stiffness of the tube was seen to vary strongly across volume defects (axial variation of the tube radius) and is assumed to result from the high crystalline defect density associated with such radial variations. These observations support recent experimental data of effective Young's modulus inferred from electrostatically-induced nanotube vibration amplitudes.
The spontaneous alignment of molecules in liquid crystalline solutions is characteristic of other materials that contain rodlike particles. We are developing a model to predict the evolution of microstructure in these...
The spontaneous alignment of molecules in liquid crystalline solutions is characteristic of other materials that contain rodlike particles. We are developing a model to predict the evolution of microstructure in these systems. Its starting point is Flory’s thermodynamic analysis of liquid crystalline phase separation. Our preferred method dispenses with the traditional lattice model in favor of a Monte Carlo simulation to calculate entropy. Some advantages and consequences of our approach are explored in this paper
We fabricated a number of top-gate graphene field-effect transistors on the ultrananocrystalline diamond (UNCD) – Si composite substrates. Raman spectroscopy, scanning electron microscopy and atomic force microscopy ...
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We fabricated a number of top-gate graphene field-effect transistors on the ultrananocrystalline diamond (UNCD) – Si composite substrates. Raman spectroscopy, scanning electron microscopy and atomic force microscopy were used to verify the quality of UNCD and graphene device channels. The thermal measurements were carried out with the “hot disk” and “laser flash” methods. It was found that graphene on UNCD devices have increased breakdown current density by ~50% compared to the reference devices fabricated on Si/SiO2. The relatively smooth surface of UNCD, as compared to other synthetic diamond films, allowed us to fabricate top gate graphene devices with the drift mobility of up to ~ 2587 cm2V−1s−1.
Experiments with monolayers of macroscopic rods indicate separation into isotropic and aligned phases at greater-than-critical concentrations. This behavior is qualitatively similar to that of rodlike liquid crystalli...
Experiments with monolayers of macroscopic rods indicate separation into isotropic and aligned phases at greater-than-critical concentrations. This behavior is qualitatively similar to that of rodlike liquid crystalline polymers, which in turn has been modelled successfully in threedimensions by Flory and Ronca. We have adapted their approach to predict the ordering of rods in two dimensions. A preliminary phase diagram is presented. The critical rod concentration at which an aligned phase can appear first is a decreasing function of rod axial ratio. Rods of a given axial ratio will phase separate at lower overall concentrations in two dimensions than in three.
Inorganic polymers are used in the formation of green compacts via sedimentation of colloidal alumina suspended in chloroform. Polymers containing highly polar components tend to produce constant density profiles of g...
Inorganic polymers are used in the formation of green compacts via sedimentation of colloidal alumina suspended in chloroform. Polymers containing highly polar components tend to produce constant density profiles of greater than 55% density, while those containing nonpolar, reactive components produce profiles with a large gradient in packing density. Density profiles describing the sedimentation behavior versus time and the final dried density of the compacts are generated via the use of gamma-ray densitometry. These polymers have the potential not only to increase green compact density but also to reduce weight losses due to “burnout” and subsequent sintering requirements by pyrolyzing to a ceramic phase.
We use cathodoluminescence (CL) mapping and Kelvin probe force microscopy (KFM) to investigate fluctuations of the InN mole fraction in InGaN films grown by radio-frequency plasma-assisted molecular beam epitaxy. Both...
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