To study the behavior of optic axons to continuously changing concentrations of their substrate, explants from embryonic retina were placed across gradients of retinal basal lamina proteins and merosin. The following growth patterns of axons in response to the substrate gradients were found: (1) Axons that grew up gradients, i.e., from low to high substrate concentrations, became longer and les...

We have previously demonstrated temporal gradients in shear stress stimulate endothelial cell proliferation, whereas spatial gradients do not. In the present study, the extracellular signal-regulated kinases 1 and 2 (ERK1/2) pathway was investigated as a possible mediator for the promitogenic effect of temporal gradients. The sudden expansion flow chamber (SEFC) model was used to differentiate ...

BACKGROUND Considerable discrepancies between Doppler and catheter gradients caused by localized gradients and pressure recovery have been reported for normal bileaflet aortic valve prostheses. METHODS AND RESULTS To examine whether this Doppler-catheter gradient relation is affected by prosthetic valve malfunction, a 19-mm CarboMedics aortic valve was simultaneously studied with continuous-w...

In this paper, optimal distributed control of the time-dependent Navier-Stokes equations is considered. The control problem involves the minimization of a measure of the distance between the velocity field and a given target velocity field. A mixed numerical method involving a quasi-Newton algorithm, a novel calculation of the gradients and an inhomogeneous Navier-Stokes solver, to find the opt...

We present a study of internal stellar population gradients in early-type cluster galaxies. Using the VLT VIMOS integral field unit, we observed 19 galaxies in the core of the Shapley Supercluster (z = 0.048). The radial trends in nine absorption lines (HδF to Fe5406) were measured to the effective radius for 14 galaxies, from which we derived the gradients in age, total metallicity and α-eleme...

The move from hand-designed to learned optimizers in machine learning has been quite successful for gradient-based and -free optimizers. When facing a constrained problem, however, maintaining feasibility typically requires a projection step, which might be computationally expensive and not differentiable. We show how the design of projection-free convex optimization algorithms can be cast as a...

Goal-conditional policies allow reinforcement learning agents to pursue specific goals during different episodes. In addition to their potential to generalize desired behavior to unseen goals, such policies may also help in defining options for arbitrary subgoals, enabling higher-level planning. While trying to achieve a specific goal, an agent may also be able to exploit information about the ...

In this paper we study the problem of learning the gradient function with application to variable selection and determining variable covariation. Firstly, we propose a novel unifying framework for coordinate gradient learning from the perspective of multi-task learning. Various variable selection algorithms can be regarded as special instances of this framework. Secondly, we formulate the dual ...