Abstract. We derive pointwise a posteriori residual-based error estimates for finite element solutions to the Stokes equations in polyhedral domains. The estimates relies on the regularity of the of Stokes equations and provide an upper bound for the pointwise error in the velocity field on polyhedral domains. Whereas the estimates provide upper bounds for the pointwise error in the gradient of...

The pseudostress-velocity formulation of the stationary Stokes problem allows a Raviart-Thomas mixed finite element formulation with quasi-optimal convergence and some superconvergent reconstruction of the velocity. This local postprocessing gives rise to some averaging a posteriori error estimator with explicit constants for reliable error control. Standard residual-based explicit a posteriori...

We report on detailed laboratory experiments designed to illustrate the frictional behavior of granular volcanic debris. The materials include pyroclastic flow debris from Soufrière Hills Volcano, Montserrat, and from Stromboli Volcano, Italy, and lahar deposits from Mount St. Helens. Experiments were conducted in a servo-controlled, double-direct shear apparatus under conditions of displacemen...

The purpose of this study was to characterize automatic remote couch adjustment and to assess the accuracy of automatic couch corrections following localization with cone-beam CT (CBCT). Automatic couch movement was evaluated through passive reflector markers placed on a phantom, tracked with an optical tracking system (OTS). Repeated couch movements in the lateral, cranial/caudal, and vertical...

Pulsed wave 2 MHz Doppler with acoustical focusing was used to obtain blood flow velocity recordings through the intact cranium in 11 patients with occlusive disease of major intracranial arteries. Increased blood flow velocities were recorded from stenoses of the carotid siphon and of the middle cerebral, anterior cerebral and basilar arteries. A clear, inverse relationship existed between ang...

In this report, we introduce a new wave-equation method of migration velocity analysis (MVA). The method is based on the linear relation that can be established between a perturbation in the migrated image and the generating perturbation in the slowness function. Our method consists of two steps: we first improve the focusing of the migrated image and then iteratively update the velocity model ...

With regard to homeoidally striated Jacobi ellipsoids (Caimmi & Marmo 2005), a unified theory of systematically rotating and peculiar motions is developed, where both real and imaginary rotation (around a fixed axis) are considered. The effect of positive or negative residual motion excess, is shown to be equivalent to an additional real or imaginary rotation, respectively. Then it is realized ...

OBJECTIVES A duplex ultrasound study was performed to investigate morphological and hemodynamic patterns of carotid stenoses treated by endarterectomy with patch closure versus stenting. MATERIALS AND METHOD Twenty-nine carotid stenoses were treated with stenting and 65 with patch closure. Duplex ultrasound parameters (luminal diameter, mm; peak systolic velocity and end-diastolic velocity, c...

I present a simple method for computing angle-domain Common Image Gather (CIG) using prestack reverse time migration. The proposed method is an extension of the method proposed by Rickett and Sava (2001) to compute CIGs by downward-continuation shotprofile migration. I demonstrate with a synthetic example the use of the CIG gathers for migration velocity updating. A challenge for imaging both o...

Image-domain wavefield tomography is a technique that reconstructs the velocity model by extracting information from migrated images. In time-lag extended images, velocity model accuracy can be evaluated by reflection focusing error, which represents the traveltime residual in the image domain. The model is updated by minimizing an objective function similar to the one used by wave-equation tra...