34,326 research outputs found
Dynamics of Neural Networks with Continuous Attractors
We investigate the dynamics of continuous attractor neural networks (CANNs).
Due to the translational invariance of their neuronal interactions, CANNs can
hold a continuous family of stationary states. We systematically explore how
their neutral stability facilitates the tracking performance of a CANN, which
is believed to have wide applications in brain functions. We develop a
perturbative approach that utilizes the dominant movement of the network
stationary states in the state space. We quantify the distortions of the bump
shape during tracking, and study their effects on the tracking performance.
Results are obtained on the maximum speed for a moving stimulus to be
trackable, and the reaction time to catch up an abrupt change in stimulus.Comment: 6 pages, 7 figures with 4 caption
Phantom Mimicry on the Normal Branch of a DGP-inspired Braneworld Scenario with Curvature Effect
It has been shown recently that phantom-like effect can be realized on the
normal branch of the DGP setup without introduction of any phantom matter
neither in the bulk nor on the brane and therefore without violation of the
null energy condition. It has been shown also that inclusion of the
Gauss-Bonnet term in the bulk action modifies this picture via curvature
effects. Here, based on the Lue-Starkman conjecture on the dynamical screening
of the brane cosmological constant in the DGP setup, we extend this proposal to
a general DGP-inspired model that stringy effects in the
ultra-violet sector of the theory are taken into account by inclusion of the
Gauss-Bonnet term in the bulk action. We study cosmological dynamics of this
setup, especially its phantom-like behavior and possible crossing of the
phantom divide line especially with a non-minimally coupled quintessence field
on the brane. In this setup, scalar field and curvature quintessence are
treated in a unified framework.Comment: 25 Figures, To appear in MPL
Remarks on hard Lefschetz conjectures on Chow groups
We propose two conjectures of Hard Lefschetz type on Chow groups and prove
them for some special cases. For abelian varieties, we shall show they are
equivalent to well-known conjectures of Beauville and Murre.Comment: to appear in Sciences in China, Ser. A Mathematic
Semi-leptonic and Non-leptonic meson decays to charmed mesons
We study the semi-leptonic and non-leptonic weak decays which are
governed by the transitions. The branching ratios, CP
asymmetries (CPA) and polarization fractions (FA) of non-leptonic decays are
investigated in the factorization approximation. The
form factors are estimated in the Salpeter method. Our estimation on branching
ratios generally agree with the existent experimental data. For CPA and
polarizations, comparisons among the FA results, the perturbative QCD
predictions and experimental data are made.Comment: 8 pages, 1 figures, 5 table
Two Dimensional Quantum Mechanical Modeling of Nanotransistors
Quantization in the inversion layer and phase coherent transport are
anticipated to have significant impact on device performance in 'ballistic'
nanoscale transistors. While the role of some quantum effects have been
analyzed qualitatively using simple one dimensional ballistic models, two
dimensional (2D) quantum mechanical simulation is important for quantitative
results. In this paper, we present a framework for 2D quantum mechanical
simulation of a nanotransistor / Metal Oxide Field Effect Transistor (MOSFET).
This framework consists of the non equilibrium Green's function equations
solved self-consistently with Poisson's equation. Solution of this set of
equations is computationally intensive. An efficient algorithm to calculate the
quantum mechanical 2D electron density has been developed. The method presented
is comprehensive in that treatment includes the three open boundary conditions,
where the narrow channel region opens into physically broad source, drain and
gate regions. Results are presented for (i) drain current versus drain and gate
voltages, (ii) comparison to results from Medici, and (iii) gate tunneling
current, using 2D potential profiles. Methods to reduce the gate leakage
current are also discussed based on simulation results.Comment: 12 figures. Journal of Applied Physics (to appear
Phase diagram of Eu magnetic ordering in Sn-flux-grown Eu(FeCo)As single crystals
The magnetic ground state of the Eu moments in a series of
Eu(FeCo)As single crystals grown from the Sn flux has
been investigated in detail by neutron diffraction measurements. Combined with
the results from the macroscopic properties (resistivity, magnetic
susceptibility and specific heat) measurements, a phase diagram describing how
the Eu magnetic order evolves with Co doping in
Eu(FeCo)As is established. The ground-state magnetic
structure of the Eu spins is found to develop from the A-type
antiferromagnetic (AFM) order in the parent compound, via the A-type canted AFM
structure with some net ferromagnetic (FM) moment component along the
crystallographic direction at intermediate Co doping levels,
finally to the pure FM order at relatively high Co doping levels. The ordering
temperature of Eu declines linearly at first, reaches the minimum value of
16.5(2) K around = 0.100(4), and then reverses upwards with
further Co doping. The doping-induced modification of the indirect
Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the Eu moments,
which is mediated by the conduction electrons on the (Fe,Co)As
layers, as well as the change of the strength of the direct interaction between
the Eu and Fe moments, might be responsible for the change of the
magnetic ground state and the ordering temperature of the Eu sublattice. In
addition, for Eu(FeCo)As single crystals with 0.10
0.18, strong ferromagnetism from the Eu
sublattice is well developed in the superconducting state, where a spontaneous
vortex state is expected to account for the compromise between the two
competing phenomena.Comment: 10 pages, 9 figure
Exact Spin and Pseudo-Spin Symmetric Solutions of the Dirac-Kratzer Problem with a tensor potential via Laplace Transform Approach
Exact bound state solutions of the Dirac equation for the Kratzer potential
in the presence of a tensor potential are studied by using the Laplace
transform approach for the cases of spin- and pseudo-spin symmetry. The energy
spectra is obtained in the closed form for the relativistic as well as
non-relativistic cases including the Coulomb potential. It is seen that our
analytical results are in agrement with the ones given in literature. The
numerical results are also given in a table for different parameter values.Comment: 8 page
Building Extraction from Very High Resolution Aerial Imagery Using Joint Attention Deep Neural Network
Automated methods to extract buildings from very high resolution (VHR) remote sensing data have many applications in a wide range of fields. Many convolutional neural network (CNN) based methods have been proposed and have achieved significant advances in the building extraction task. In order to refine predictions, a lot of recent approaches fuse features from earlier layers of CNNs to introduce abundant spatial information, which is known as skip connection. However, this strategy of reusing earlier features directly without processing could reduce the performance of the network. To address this problem, we propose a novel fully convolutional network (FCN) that adopts attention based re-weighting to extract buildings from aerial imagery. Specifically, we consider the semantic gap between features from different stages and leverage the attention mechanism to bridge the gap prior to the fusion of features. The inferred attention weights along spatial and channel-wise dimensions make the low level feature maps adaptive to high level feature maps in a target-oriented manner. Experimental results on three publicly available aerial imagery datasets show that the proposed model (RFA-UNet) achieves comparable and improved performance compared to other state-of-the-art models for building extraction
Role of axin in nerve growth factor-stimulated neurite outgrowth
The role of integrin-linked kinase (ILK), a kinase that is involved in various cellular processes, including adhesion and migration, has not been studied in primary neurons. Using mRNA dot blot and Western blot analysis of ILK in rat and human brain tissue, we found that ILK is expressed in various regions of the CNS. Immunohistochemical and immunocytochemical techniques revealed granular ILK staining that is enriched in neurons and colocalizes with the 1 integrin subunit. The role of ILK in neurite growth promotion by NGF was studied in rat pheochromocytoma cells and dorsal root ganglion neurons using a pharmacological inhibitor of ILK (KP-392) or after overexpres-sion of dominant-negative ILK (ILK-DN). Both molecular and pharmacological inhibition of ILK activity significantly reduced NGF-induced neurite outgrowth. Survival assays indicate that KP-392-induced suppression of neurite outgrowth occurred in the absence of cell death. ILK kinase activity was stimulated by NGF. NGF-mediated stimulation of phosphorylation of both AKT and the Taukinase glycogen synthase kinase-3 (GSK-3) was inhibited in the presence of KP-392 and after overexpression of ILK-DN. Consequently, ILKinhibition resulted in an increase in the hyperphosphorylation of Tau , a substrate of GSK-3. Together these findings indicate that ILK is an important effector in NGF-mediated neurite outgrowth. The role of integrin-linked kinase (ILK), a kinase that is involved in various cellular processes, including adhesion and migration, has not been studied in primary neurons. Using mRNA dot blot and Western blot analysis of ILK in rat and human brain tissue, we found that ILK is expressed in various regions of the CNS. Immunohistochemical and immunocytochemical techniques revealed granular ILK staining that is enriched in neurons and colocalizes with the 1 integrin subunit. The role of ILK in neurite growth promotion by NGF was studied in rat pheochromocytoma cells and dorsal root ganglion neurons using a pharmacological inhibitor of ILK (KP-392) or after overexpres- sion of dominant-negative ILK (ILK-DN). Both molecular and pharmacological inhibition of ILK activity significantly reduced NGF- induced neurite outgrowth. Survival assays indicate that KP-392-induced suppression of neurite outgrowth occurred in the absence of cell death. ILK kinase activity was stimulated by NGF. NGF-mediated stimulation of phosphorylation of both AKT and the Tau kinase glycogen synthase kinase-3 (GSK-3) was inhibited in the presence of KP-392 and after overexpression of ILK-DN. Consequently, ILK inhibition resulted in an increase in the hyperphosphorylation of Tau , a substrate of GSK-3. Together these findings indicate that ILK is an important effector in NGF-mediated neurite outgrowth
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