Corrosion Embrittlement of Duralumin V : Results of Weather-Exposure Tests

In a series of weather exposure tests of sheet duralumin, upon which accelerated corrosion tests in the laboratory by the wet-and-dry corrosion method in a sodium chloride solution has already been carried out, a close parallelism between the results of the two kinds of tests was found to exist. The exposure tests showed that the lack of permanence of sheet duralumin is largely, if not entirely, due to corrosion. A corrosion attack of an intercrystalline nature is very largely responsible for the degree of embrittlement produced. The rate of embrittlement was greatly accelerated by a marine atmosphere and by the tropical climate. Variations in corrosion and embrittlement are noted in relation to heat treatment, cold working, and types of protective coatings

Corrosion Embrittlement of Duralumin III Effect of the Previous Treatment of Sheet Material on the Susceptibility to This Type of Corrosion

As a result of testing, it was determined that control of the rate of quenching and the avoidance of accelerated aging by heating are the only means of modifying duralumin itself so as to minimize the intercrystalline form of corrosive attack. It is so simple a means that it should be adopted even though it may not completely prevent, but only reduce, this form of corrosive attack. By so doing, the need for protection of the surface is less urgent

Ropelength of tight polygonal knots

A physical interpretation of the rope simulated by the SONO algorithm is presented. Properties of the tight polygonal knots delivered by the algorithm are analyzed. An algorithm for bounding the ropelength of a smooth inscribed knot is shown. Two ways of calculating the ropelength of tight polygonal knots are compared. An analytical calculation performed for a model knot shows that an appropriately weighted average should provide a good estimation of the minimum ropelength for relatively small numbers of edges.Comment: 27 pages, to appear in "Physical and Numerical Models in Knot Theory and their Application to the Life Sciences

Knot Tightening By Constrained Gradient Descent

We present new computations of approximately length-minimizing polygons with fixed thickness. These curves model the centerlines of "tight" knotted tubes with minimal length and fixed circular cross-section. Our curves approximately minimize the ropelength (or quotient of length and thickness) for polygons in their knot types. While previous authors have minimized ropelength for polygons using simulated annealing, the new idea in our code is to minimize length over the set of polygons of thickness at least one using a version of constrained gradient descent. We rewrite the problem in terms of minimizing the length of the polygon subject to an infinite family of differentiable constraint functions. We prove that the polyhedral cone of variations of a polygon of thickness one which do not decrease thickness to first order is finitely generated, and give an explicit set of generators. Using this cone we give a first-order minimization procedure and a Karush-Kuhn-Tucker criterion for polygonal ropelength criticality. Our main numerical contribution is a set of 379 almost-critical prime knots and links, covering all prime knots with no more than 10 crossings and all prime links with no more than 9 crossings. For links, these are the first published ropelength figures, and for knots they improve on existing figures. We give new maps of the self-contacts of these knots and links, and discover some highly symmetric tight knots with particularly simple looking self-contact maps.Comment: 45 pages, 16 figures, includes table of data with upper bounds on ropelength for all prime knots with no more than 10 crossings and all prime links with no more than 9 crossing

Effect of Eccentric Contraction-Induced Injury on Individual Quadriceps Muscles: Impact on Muscle Activation, Joint Torque and Motor Control

Research has shown that exercise-induced muscle injury can cause 25-50% reductions in maximal joint torque. However, it is unknown whether individual muscles of a synergist group are injured to the same extent following injury. We hypothesized that the extent of injury among synergistic muscles is not uniform, and the primary cause of the weakness stems from the failure of muscle and not the ability of the nervous system to activate the muscle. We also presumed that muscle injury would alter balance (postural sway) and quadricep muscle activation patterns (electromyography [EMG]) during locomotion. 15 healthy sedentary or recreationally active male subjects between 18 and 35 years old completed the study. Subjects performed either downhill running (DHR) on a treadmill for 60 min to induce injury (n=8) or level treadmill walking for 30 min as control (n=7). Before and after (immediately and 2-days) exercise, we measured 1) maximal voluntary contraction (MVC) torque of quadricep muscles (QMs), 2) torque produced by vastus medialis (VM), rectus femoris (RF) and vastus lateralis (VL) via electrical stimulation (20 and 80 Hz), 3) soreness of individual QMs, 4) QMs EMG root mean square (RMS) during running and MVCs, and 5) standing postural sway. MVC 90° torque was significantly reduced immediately (25.3%) and 2-days (14.0%) after DHR, whereas torque was unchanged after level walking. After DHR (immediately and 2-days), MVC RMS across all three quadriceps muscles was significantly reduced by 16.8% immediately following injury. There was a 13.2% decrease in stimulated torque (20 & 80 Hz) collapsed across all muscles for the injury group immediately post and a decrease of 9.1% at 48H following. At 48 hours, the VL experienced greater soreness than RF and VM. Running RMS of the knee extensor muscles increased immediately after DHR. Postural sway increased immediately after DHR and decreased in the control group at 2-days. In conclusion, DHR caused the differential injury of the QMs, and reduced activation (i.e., RMS) of the quadriceps and force depression (i.e., 20 & 80 Hz torque) account for the decreases in MVC torque after DHR. In addition, muscle injury from DHR disrupted standing balance and normal muscle activation patterns during running

Thinking Disgust Plural

The paper explores the connections between disgust and contempt, arguing that contempt as a visceral and intellectual affect emerges out of a knowledge of disgust. Just as contempt can constitute a polished performance, so too disgusting objects can be transformed into art.Â