Lehigh University

About: Lehigh University is a education organization based out in Bethlehem, Pennsylvania, United States. It is known for research contribution in the topics: Catalysis & Fracture mechanics. The organization has 12684 authors who have published 26550 publications receiving 770061 citations.

Planning Dynamically Feasible Trajectories for Quadrotors Using Safe Flight Corridors in 3-D Complex Environments

Abstract: There is extensive literature on using convex optimization to derive piece-wise polynomial trajectories for controlling differential flat systems with applications to three-dimensional flight for Micro Aerial Vehicles. In this work, we propose a method to formulate trajectory generation as a quadratic program (QP) using the concept of a Safe Flight Corridor (SFC). The SFC is a collection of convex overlapping polyhedra that models free space and provides a connected path from the robot to the goal position. We derive an efficient convex decomposition method that builds the SFC from a piece-wise linear skeleton obtained using a fast graph search technique. The SFC provides a set of linear inequality constraints in the QP allowing real-time motion planning. Because the range and field of view of the robot's sensors are limited, we develop a framework of Receding Horizon Planning , which plans trajectories within a finite footprint in the local map, continuously updating the trajectory through a re-planning process. The re-planning process takes between 50 to 300 ms for a large and cluttered map. We show the feasibility of our approach, its completeness and performance, with applications to high-speed flight in both simulated and physical experiments using quadrotors.

Observations on coastal erosion in bermuda and measurements of the boring rate of the sponge, cliona lampa1,2

Abstract: Measured profiles of the submerged portion of the steep cliffs that ring Harrington Sound, Bermuda, show that they are undercut as much as 4 to 5 m by a notch whose flat roof coincides closely with the level of extreme low tides. Nips, intertidal indentations with sloping roofs, are not present. Because of the largely subtidal position of the notch, the morphology of the undercut region, and the restricted wave energy, wave cutting is ruled out and bioerosion is proposed as the mechanism of undercutting. Bioerosion is suggested as a term for the removal of consolidated mineral or lithic substrate by the direct action of organisms. Observations of the emerged and submerged carbonate coastline of Bermuda reveal that organisms of many types alter the exposed rock surface from the upper reaches of the spray zone to depths well below sea level by processes that vary with degree of exposure, tidal range, rock type, organic community, and probably other ecological variables. A series of experiments with common rock-destroying organisms has been initiated. Experiments in the laboratory and under natural conditions show that Cliona lampa, a boring sponge, is capable of removing as much as 6 to 7 kg of material from 1 m2 of carbonate substrate in 100 days. This corresponds to an erosion rate of calcarenite of more than 1 cm/year. If previous estimates are correct (that 90% of the boring by C. lampa is mechanical and not chemical), then 5 to 6 kg of fine-grained carbonate detritus can be supplied from 1 m2 of sponge-infected substrate in 100 days.

The Surface Crack Problem for a Plate With Functionally Graded Properties

Abstract: In this study the plane elasticity problem for a nonhomogeneous layer containing a crack perpendicular to the boundaries is considered. It is assumed that the Young's modulus of the medium varies continuously in the thickness direction. The problem is solved under three different loading conditions, namely fixed grip, membrane loading, and bending applied to the layer away from the crack region. Mode I stress intensity factors are presented for embedded as well as edge cracks for various values of dimensionless parameters representing the size and the location of the crack and the material nonhomogeneity. Some sample results are also given for the crack-opening displacement and the stress distribution.

Determination of Degree of Substitution of Formyl Groups in Polyaldehyde Dextran by the Hydroxylamine Hydrochloride Method

Abstract: Colorimetric or potentiometric titration of the aldehyde residues in polyaldehyde dextran by the hydroxylamine hydrochloride/sodium hydroxide method has been found to be a convenient and accurate method to determine formyl content. Nitrogen combustion analyses on the isolated oximes confirmed the titrametric results.