A new technique for modelling biological signals as a linear combination of non-orthogonal Gabor logons is described. The technique has been applied to two types of signals, Event-Related Potentials (ERPs) and temporo...
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A thorough understanding of fundamental microwave absorption mechanisms in ionic crystalline solids is important for microwave sintering of ceramics, as well as the design of high speed electronic packaging, advanced ...
A thorough understanding of fundamental microwave absorption mechanisms in ionic crystalline solids is important for microwave sintering of ceramics, as well as the design of high speed electronic packaging, advanced radomes, etc. Of particular importance to these applications are how the density and type of crystalline defects affect the dominant microwave absorption mechanisms. We have designed experiments to measure microwave absorption in NaCl samples with controlled variations in defect conditions(pure, point defects, dislocations and grain boundaries) at different temperatures (20-400 °C) and frequencies (2-20 GHz). Initial results are reported and discussed.
Multi-element synthetic aperture imaging methods suitable for applications with severe cost and size limitations are explored. Array apertures are synthesized using an active multi-element receive subaperture and a mu...
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Multi-element synthetic aperture imaging methods suitable for applications with severe cost and size limitations are explored. Array apertures are synthesized using an active multi-element receive subaperture and a multi-element defocused transmit subaperture. The performance of multi-element methods has been tested and compared to conventional imagers through measurements with a 3.5 MHz, 128-element transducer array on different gel phantoms. The multi-element synthetic aperture methods achieve higher electronic signal to noise ratio and better contrast resolution than conventional synthetic aperture techniques, approaching conventional phased array performance
A new technique for modelling biological signals as a linear combination of non-orthogonal Gabor logons is described. The technique has been applied to two types of signals, event-related potentials (ERPs) and temporo...
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A new technique for modelling biological signals as a linear combination of non-orthogonal Gabor logons is described. The technique has been applied to two types of signals, event-related potentials (ERPs) and temporomandibular joint (TMJ) clicks. Examination of time-frequency representations of these signals revealed that they appear to consist of a small number of localized energy concentrations. Attempts to capture this apparent low dimensionality with the standard orthogonal Gabor expansion and the standard wavelet transform were unsuccessful. However, the non-orthogonal Gabor decomposition method described in this paper provides a compact, accurate signal representation and the parameters provide a good basis for ERP category and TMJ click classification.< >
An optical scattering method, which measures the size, number, and type of microemboli located in flowing whole blood, is described. A perturbation solution to the one speed radiative transport equation is used to mod...
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An optical scattering method, which measures the size, number, and type of microemboli located in flowing whole blood, is described. A perturbation solution to the one speed radiative transport equation is used to model the scattering geometry. The approximate two-parameter phase function is used to investigate scattering characteristics of microemboli. The nature of microemboli is determined by comparing the scattered intensity ratio in two forward directions, while the size and number are determined by considering intensities scattered perpendicularly to the incident direction. This method has been tested with several sizes of polystyrene spheres, air bubbles, and blood dots. The results showed excellent agreement with calculations.
This paper presents a comparison of H/sub /spl infin////spl mu/-synthesis sliding-mode that was done for heading and depth control of the Draper Laboratory/MIT Sea Grant Sea Squirt autonomous underwater vehicle (AUV)....
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This paper presents a comparison of H/sub /spl infin////spl mu/-synthesis sliding-mode that was done for heading and depth control of the Draper Laboratory/MIT Sea Grant Sea Squirt autonomous underwater vehicle (AUV). The approximate decoupling of the AUV heading and depth dynamics allowed us to have decoupled heading and depth designs for both the H/sub /spl infin////spl mu/-synthesis and the sliding-mode methodologies. The H/sub /spl infin////spl mu/-synthesis based controllers and the sliding-mode based controllers were implemented and tested by using a simulation of the AUV full order nonlinear model (including thruster and sensor dynamics). We analyzed the performance of the controllers (for a simultaneous depth and maneuver) over the approximate range of axial velocities commanded by the AUV. The performance of the controllers in the face of additive sensor noise was also analyzed.
Raman spectroscopy and x-ray diffraction are used to characterize Gallium Nitride (GaN) films grown on (100) Gallium Arsenide (GaAs) substrates. Reflection X-ray diffraction data from (200) planes of GaAs and cubic Ga...
Raman spectroscopy and x-ray diffraction are used to characterize Gallium Nitride (GaN) films grown on (100) Gallium Arsenide (GaAs) substrates. Reflection X-ray diffraction data from (200) planes of GaAs and cubic GaN are presented. The linewidth of the cubic GaN diffraction peak is shown to be a strong function of the growth temperature. Raman spectra are presented for a series of samples grown at different temperatures. Raman scattering is characterized by strong peaks at 560 cm-1 and at 736 cm-1, corresponding to TO and LO phonon modes of cubic GaN, respectively. An additional, unexplained feature at 768 cm-1 is clearly observed in Raman spectra of c-GaN samples grown at lower temperatures. The polarization dependence of the intensity of the GaN LO phonon mode is presented and compared with the GaAs LO phonon mode to establish the relative orientation of the c-GaN epitaxy on GaAs.
Given an arbitrary telecommunications network N our goal is to find the minimum cost for equipment which will enable N to survive an arbitrary link fault. We consider uni-directional and bi-directional ring technologi...
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Given an arbitrary telecommunications network N our goal is to find the minimum cost for equipment which will enable N to survive an arbitrary link fault. We consider uni-directional and bi-directional ring technologies. Basically, our goal is to find minimum cost ring covers for any network N, where a ring cover is a set C of rings such that every link in N is covered by (i.e. part of) at least one ring in C. If a network N is augmented with enough equipment to support a given ring cover C, it can respond to a link failure immediately (and automatically) by routing the disrupted traffic through surviving links in the ring that covers the failed link. We describe an efficient algorithm to find a minimum cost ring cover for uni-directional transmission rings under simplifying assumptions. This algorithm offers a useful heuristic for computing low cost ring covers for existing networks and actual cost functions. We also provide efficient heuristics to find nearly minimum cost ring covers for bi-directional transmission rings. We show that certain versions of the bi-directional problem are NP-complete, hence (presumably) no efficient algorithm exists that always finds a minimum cost ring cover. However, our heuristics perform well in practice.
The authors characterize electrostatic and other polymer-polymer interactions within an ultracentrifuge cell using a new electrochemical transport model. Applying conservation of mass and momentum of solutes and solve...
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The authors characterize electrostatic and other polymer-polymer interactions within an ultracentrifuge cell using a new electrochemical transport model. Applying conservation of mass and momentum of solutes and solvent, and Maxwell's equations valid in the electroquasistatic limit, together with initial and boundary conditions on solute (and electrolyte) distribution, the authors predict the transient (nonequilibrium) and equilibrium solute (and electrolyte) distributions, net charge density, electric field, and electrostatic potential profiles. This model represents a significant advance ever the Lamm equation (and its extensions) (H. Fujita, 1962), which describe polymer-polymer interactions phenomenologically (using empirical virial coefficients) (L.W. Nichol et al., 1967).< >
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