Aeronautical engineering: A continuing bibliography with indexes, supplement 100

This bibliography lists 295 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System in August 1978

Electromechanical System Integration for a Powered Upper Extremity Orthosis

Wearable robotics for assistance and rehabilitation are not yet considered commercially mainstream products, and as a result have not yet seen advanced controls systems and interfaces. Consequently, the available technology is mostly adapted from systems used in parallel technologies, rather than custom applications intended for human use. This study concerns itself with the design and development of a custom control system for a 2-degree of freedom powered upper extremity orthosis capable of driving elbow flexion/extension 135º and humeral rotation 95º . The orthosis has been evaluated for use as both a long-term assistive technology device for persons with disabilities, and as a short-term rehabilitative tool for persons recovering injury. The target demographics for such a device vary in age, cognitive ability and physical function, thus requiring several input parameters requiring consideration. This study includes a full evaluation of the potential users of the device, as well as parameter considerations that are required during the design phase. The final control system is capable of driving each DOF independently or simultaneously, for a more realistic and natural coupled-motion, with proportional control by pulse-width modulation. The dual-axis joystick interface wirelessly transmits to the 1.21 pound control pack which houses a custom microcontroller-driven PCB and 1800 milliamp-hour lithium-ion rechargeable battery capable of delivering 4 hours of running time. Upon integration with the 2 DOF orthosis device, a user may complete full range of motion with up to 5 pounds in their hand in less than 7 seconds, providing full functionality to complete acts of daily living, thus improving quality of life

In Defense of Wireless Carrier Sense

Carrier sense is often used to regulate concurrency in wireless medium access control (MAC) protocols, balancing interference protection and spatial reuse. Carrier sense is known to be imperfect, and many improved techniques have been proposed. Is the search for a replacement justified? This paper presents a theoretical model for average case two-sender carrier sense based on radio propagation theory and Shannon capacity. Analysis using the model shows that carrier sense performance is surprisingly close to optimal for radios with adaptive bitrate. The model suggests that hidden and exposed terminals usually cause modest reductions in throughput rather than dramatic decreases. Finally, it is possible to choose a fixed sense threshold which performs well across a wide range of scenarios, in large part due to the role of the noise floor. Experimental results from an indoor 802.11 testbed support these claims

Roman Domination in Complementary Prism Graphs

A Roman domination function on a complementary prism graph GGc is a function f : V [ V c ! {0, 1, 2} such that every vertex with label 0 has a neighbor with label 2. The Roman domination number R(GGc) of a graph G = (V,E) is the minimum of Px2V [V c f(x) over such functions, where the complementary prism GGc of G is graph obtained from disjoint union of G and its complement Gc by adding edges of a perfect matching between corresponding vertices of G and Gc. In this paper, we have investigated few properties of R(GGc) and its relation with other parameters are obtaine

Four-bar linkage synthesis using non-convex optimization

Ce mémoire présente une méthode pour synthétiser automatiquement des mécanismes articulés à quatre barres. Un logiciel implémentant cette méthode a été développé dans le cadre d’une initiative d’Autodesk Research portant sur la conception générative. Le logiciel prend une trajectoire en entrée et calcule les paramètres d’un mécanisme articulé à quatre barres capable de reproduire la même trajectoire. Ce problème de génération de trajectoire est résolu par optimisation non-convexe. Le problème est modélisé avec des contraintes quadratiques et des variables réelles. Une contrainte redondante spéciale améliore grandement la performance de la méthode. L’expérimentation présentée montre que le logiciel est plus rapide et précis que les approches existantes.This thesis presents a method to automatically synthesize four-bar linkages. A software implementing the method was developed in the scope of a generative design initiative at Autodesk. The software takes a path as input and computes the parameters of a four-bar linkage able to replicate the same path. This path generation problem is solved using non-convex optimization. The problem is modeled with quadratic constraints and real variables. A special redundant constraint greatly improves the performance of the method. Experiments show that the software is faster and more precise than existing approaches

Optimization for Commercialization of A Two Degree of Freedom Powered Arm Orthosis

In the United States, more than 18 million people suffer from upper extremity injury. This population is in need of a device both to aid in the completion of activities of daily living (eating and grooming), as well as to provide daily muscular therapy. To assist persons suffering from disabling upper extremity neuromuscular diseases, this thesis concerned the redesign of a powered arm brace from a proof-of-concept design to a more functional, marketable product. The principles of Design for Manufacturability and Assembly (DFMA) were employed as part of the design methodology to create a product that could be scaled into production. Additionally, numerical analyses including Finite Element Analysis (FEA) were completed to prove the both the safety and structural integrity of the orthosis in computer simulations. The design was then successfully tested with marked improvement over the previous design, including a 58% reduction in weight, decreased manufacturing costs, and a significant improvement in functionality and comfort

Discrete Mathematics and Symmetry

Some of the most beautiful studies in Mathematics are related to Symmetry and Geometry. For this reason, we select here some contributions about such aspects and Discrete Geometry. As we know, Symmetry in a system means invariance of its elements under conditions of transformations. When we consider network structures, symmetry means invariance of adjacency of nodes under the permutations of node set. The graph isomorphism is an equivalence relation on the set of graphs. Therefore, it partitions the class of all graphs into equivalence classes. The underlying idea of isomorphism is that some objects have the same structure if we omit the individual character of their components. A set of graphs isomorphic to each other is denominated as an isomorphism class of graphs. The automorphism of a graph will be an isomorphism from G onto itself. The family of all automorphisms of a graph G is a permutation group

The mechanisms of wet clutch friction behaviour

Wet clutches are used in automatic transmissions to bring about gear changes and also to reduce energy loss in the torque converter. These friction devices are susceptible to stick-slip effects, which result in the vehicle giving an unsteady ride. Stick-slip effects can be avoided by ensuring the wet clutch and lubricant combination produces a friction coefficient that increases with sliding speed. This friction characteristic is achieved by using a specific material on one of the two clutch surfaces and by using certain surface active chemicals, which are added to the lubricant. Although wet clutches have been studied throughout the industry for many decades, the mechanism of the generated friction is still not fully understood. In this thesis the friction mechanisms are clarified by the experimental study of the wet clutch in terms of its real area of contact, its flash temperatures and the friction characteristics, which are measured over a broad range of conditions. These results are used along with theoretical calculations to first clarify the lubrication regime, which is found to be predominantly boundary due to the roughness of the friction material and the small size of the contact units formed. The generated friction is then attributed to surface active additives, which form solid-like films on the clutch surfaces. These friction characteristics can be modified by varying the nature of the solid-like film, and when a close-packed film is formed, this displays the friction increasing with speed characteristic due to an activated shearing mechanism, which is linked to the speed of molecular rearrangement at the surface