We consider an inverse problem of determining a spatially varying factor in a source term in a nonstationary linearized Navier-Stokes equations by observation data in an arbitrarily fixed sub-domain over some time interval. We prove the Lipschitz stability provided that the t-dependent factor satisfies a non-degeneracy condition. Our proof based on a new Carleman estimate for the Navier-Stokes ...

INTRODUCTION: O-Space parallel imaging combines a Z2 gradient field with conventional radial k-space trajectories to perform highly-efficient parallel imaging [1]. Because the Z2 field varies as r2 = x2+y2 in the axial plane, it provides spatial encoding that is complementary to that obtained from a circumferential surface coil array. However, non-linear projection encoding invites the explorat...

Current American design provisions treat unstiffened elements under stress gradients as if they were uniformly compressed for effective width calculations. Australian, British, and European design provisions allow accurate calculation of the elastic buckling coefficient, however, the same effective width equation for compressed elements is used for elements with stress gradients. In all cases, ...

A Monte Carlo algorithm for extracting contours in 2D images is proposed in this paper. A multiple model Particle Filter (PF) for progressive contour growing (tracking) from a starting point is designed, accounting for the convex, noncircular form of delineated areas. The algorithm relies on image intensity gradients as measurements and requires information about four manually selected points: ...

This paper studies the problem of distributed stochastic optimization in an adversarial setting where, out of the m machines which allegedly compute stochastic gradients every iteration, an α-fraction are Byzantine, and can behave arbitrarily and adversarially. Our main result is a variant of stochastic gradient descent (SGD) which finds ε-approximate minimizers of convex functions in T = Õ ( 1...

Background Phase contrast MRI (PC-MRI) sequences conventionally use triangular and trapezoidal gradient waveforms to construct flow compensated and flow encoded (FCFE) [1] or Bipolar [2] velocity encoding gradients. This approach does not make optimal use of the available gradient hardware for all time points, but convex optimization (CVX) can be used to design minimum-duration, arbitrarily sha...

An expression for the axial current in an arbitrarily strong, slowly varying electromagnetic field is obtained. We apply this expression to the construction of the effective action for low-energy neutrino-photon interactions. Email:[email protected] Email:[email protected] 1

High reynolds number ow simulations exhibit strong gradients normal to walls and across shear layers requiring much ner resolution of the solution in some directions compared to others. To keep mesh sizes manageable for such problems, meshes with highly anisotropic elements are necessary. In this paper, a method for generating boundary layer meshes for arbitrarily complex non-manifold geometric...

We present a method for recovering time-lapse velocity changes using full waveform inversion (FWI). In a preprocessing step we invert for a single intermediate model by simultaneously minimizing the data misfit in the baseline and the monitor surveys. We record the individual FWI gradients corresponding to the baseline and the monitor datasets at each iteration of the inversion. Regions where t...

A new external velocity field for active contours is proposed. The velocity field is based on magnetostatics and hypothesised magnetic interactions between the active contour and image gradients. In this paper, we introduce the method and study its convergence capability for the recovery of shapes with complex topology and geometry, including deep, narrow concavities. The proposed active contou...