Abstract: The SuperDARN HF coherent scatter radars (Greenwald et al, 1995) provide line-of-sight (l-o-s) velocity measurements of ionospheric convection flow over the polar regions of the northern and southern hemispheres A number of techniques have been developed in order to obtain 2-D plasma flow vectors from these l-o-s observations This study entails a comparison of the ionospheric flow vectors derived using the "map-potential", and "beam-swinging" techniques with the vectors derived using the "merging" technique The merging technique is assumed to be the most accurate method of deriving local flow vectors from l-o-s velocities We can conclude that the map-potential model is significantly more successful than the beam-swinging technique at estimating both the magnitude and the direction of the large-scale ionospheric convection flow vectors The quality of the fit is dependent on time of day, with vectors observed at low latitudes in the dawn sector agreeing most closely with the merged vector flow pattern Key words Ionosphere (plasma convection; instruments and techniques) – Radio science (instruments and techniques)

Abstract: A new ultrasound technique for determining three-dimensional velocity vectors has been devised using radio frequency (RF) data from commercially available scanners. Applied to blood flow, this technique could prove useful for evaluating hemodynamics and detecting stenoses. Three orthogonal velocity vectors are computed from the RF signals of two steered beams from a single array. The in-plane velocities are determined using standard Doppler analysis, while the out-of-plane component is derived from the total velocity as computed from temporal decorrelation and the in-plane components. The technique was tested using contrast agent pumped through a flow tube. A GE Vingmed SystemV scanner with a 10 MHz linear array provided scans at beam steering angles of +/- 20 degree(s). Both Doppler velocities and temporal complex decorrelation were computed for each digitized voxel. Additional studies were done on a blood mimicking fluid and in vivo with a canine femoral artery. Vector plots were constructed to show flow for various transducer angles. Angle estimates were within 20 degree(s), and the mean error for the velocity amplitude was less than 15%. The in vivo results provided velocity estimates consistent with the literature. The proposed method, unlike current Doppler velocity measurement techniques, provides quantitative velocity information independent of transducer orientation.

Abstract: When used as the image force for active contours, the gradient has the disadvantage of having a restricted capture range. Two solutions for improving the capture range, gradient vector flow and pressure forces, were compared. Although GVF provides a good capture range, it sometimes leads to boundary delocalisation. As an alternative, pressure forces have shown promising results for histological middle-ear images. The use of open contours was also demonstrated, in addition to the usual closed contours.

Abstract: A fluid flow sensor uses Particle Image Velocimetry to plot the vector flow (20) of fluids such as the charge in an engine cylinder with data processing to determine the real center of turbulent rotation (38).

Abstract: Accurate analysis of insect brain structures in digital confocal microscopic images is valuable and important to biology research needs. The first step is to segment meaningful structures from images. Active contour model, known as snakes, is widely used for segmentation of medical images. A new class of active contour model called gradient vector flow snake has been introduced in 1998 to overcome some critical problems encountered in the traditional snake. In this paper, we use gradient vector flow snake to segment the mushroom body and the central body from the confocal microscopic insect brain images. First, an edge map is created from images by some edge filters. Second, a gradient vector flow field is calculated from the edge map using a computational diffusion process. Finally, a traditional snake deformation process starts until it reaches a stable configuration. User interface is also provided here, allowing users to edit the snake during deformation process, if desired. Using the gradient vector flow snake as the main segmentation method and assist with user interface, we can properly segment the confocal microscopic insect brain image for most of the cases. The identified mushroom and central body can then be used as the preliminary results toward a 3-D reconstruction process for further biology researches.

Abstract: We present the results of a study exploring the upper velocity limit of vector flow estimation with Heterodyned Spatial Quadrature. Since this is highly dependent on apodization, we investigated a set of apodization windows designed to explore means of extending the practical velocity range. Heterodyned Spatial Quadrature (HSQ) is a recently described vector flow technique that has been shown to provide accurate flow estimates in both the axial and lateral directions. The complex PSF created by this technique induces a modulation in the received echo of a scatterer traversing the resolution volume at a frequency proportional to the scatterer lateral velocity. We measure the rate of phase change of this modulation to provide an estimate of the lateral flow velocity component. The technique is extendible to 3D vector flow estimation with a 2D array. We expect lateral tracking methods in general to be limited by a number of factors including the PSF beam width and the system amplitude sensitivity. Using a Siemens Elegra ultrasound scanner with a 7.5 MHz linear array, we simulated flow up to 405 /spl mu/m per step in a tissue-mimicking phantom, corresponding to velocities up to 4.05 m/sec for a PRF of 10 kHz, at Doppler angles of 60/spl deg/ and 90/spl deg/. We estimated lateral velocities to within 5% relative bias up to 315 cm/sec in an f/2 geometry at a 90/spl deg/ Doppler angle. The spatial quadrature receive aperture utilized a bi-lobed Blackman apodization with a width of 1/2D, where D is the full width of the array. Computer simulations of the system under similar conditions produced lateral velocity estimates up to 303 cm/sec. As expected, the maximum estimable velocity scales with focal depth. In simulations, the same aperture estimated flow velocities up to 672 cm/sec at a focal depth of 75 mm, representing an f/5 geometry.

Abstract: We present a method for multi-parameter sensing in the application of thermal vector flow sensors. The method is based on the property that two independent signals can be obtained from a single sensing element, viz. a thermal vector flow sensor For particular applications, this reduces the number of sensors in the measurement process. It may also allow redundant measurement of physical parameters, such as temperature; these redundant measurements are important for self-diagnostics of proper operation of a measurement system. The method is applied to a bidirectional silicon flow sensor, that generates two independent signals, both being a function of the Re number and the fluid temperature. This allows both temperature and mass flow measurement by use of a single sensor

Abstract: Publisher Summary Two-dimensional flow is the special class of flow that occurs in a plane and is symmetric in the direction normal to this plane. Axisymmetric flow is the special class of flow that occurs in half-planes containing an axis of symmetry and is symmetric about this axis. For many important applications, 3D flow may be decomposed into 2D and axisymmetric components. Irrotational flow fields are commonly analyzed using a potential function. These potentials may be added together to model any 3D flow that can be decomposed into two-dimensional and axisymmetric components. Divergence-free flow fields are commonly analyzed using the Lagrange stream function for 2D flow fields. While Lagrange and Stokes stream functions cannot be immediately added together as with the potential, it is shown that they may be combined through use of a vector potential. The vector potential is advantageous for computing flux, since dimensionality is reduced from the surface integral required to evaluate this flux using the specific discharge vector to a line integral. Computing flux using a vector potential is also advantageous for a flow field with 2D and axisymmetric components, since a method to obtain closed-form solutions exists in Steward for flux through surfaces bounded by straight line segments with arbitrary orientations.

Abstract: In this paper we propose a level set method to segment MR cardiac images. Our approach is based on a coupled propagation of two cardiac contours and integrates visual information with anatomical constraints. The visual information is expressed through a gradient vector flow-based boundary component and a region term that aims at best separating the cardiac contours/regions according to their global intensity properties. In order to deal with misleading visual support, an anatomical constraint is considered that couples the propagation of the cardiac contours according to their relative distance. The resulting motion equations are implemented using a level set approach and a fast and stable numerical approximation scheme, the Additive Operator Splitting. Encouraging experimental results are provided using real data.