Index to 1981 NASA Tech Briefs, volume 6, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1981 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Polymer nematic liquid crystals :: disclination structure and interaction/

Disclinations and inversion walls in the director field of nematic thermotropic liquid crystal polymers (TLCP\u27s) are imaged at high resolution using the lamellar decoration technique of Wood and Thomas. The utility of the lamellar decoration technique has also been greatly extended by using an etch and replication technique to image the director in sections of a bulk sample. The interaction of disclinations in the presence of an applied magnetic or extensional flow field which tends to align the director is studied. At intermediate field strengths, where the disclination separation is comparable to the characteristic length for director field distortions, pairwise interaction no longer dominates, but clusters of disclinations are observed to form. The applied field suppresses fluctuations of the disclination positions which increase the topological dipole moment of a cluster while enhancing those that preserve zero dipole. The applied field tends to minimize the long range distortional energy which is proportional to the square of the dipole moment. As a result, quadrupolar (Lehmann) clusters of disclinations are commonly observed in either magnetically or extensionally flow aligned samples. Many-bodied interaction of disclinations in the absence of an applied field is studied via computer simulation, and the results agree favorably with recent experimental work. The structure of the cores of disclinations has been observed. The core size is on the order of a few molecular lengths, and its structure depends upon polymer architecture. A rigid polymer splays more within the core of a $\pi$ wedge disclination, and an excess of chain ends aggregates. A semi-flexible polymer, in contrast, bends more within the core. Hairpins are not thought to be abundant in the semi-flexible TLCP. The morphology of the TLCP semi-crystalline state has also been examined. It is observed to depend upon the relative primary crystal nucleation and crystal growth rates. The lamellar decoration morphology, where the crystalline lamellae are everywhere perpendicular to the director of the precursor nematic, is favored by rapid nucleation and slow growth. This morphology is unique to TLCP\u27s, but other morphologies are possible. Spherulites have also been grown from the nematic melt. Their growth is favored by slow nucleation and rapid growth

Design of a miniaturized work-cell for micro-manipulation

The paper describes the design and development of a miniaturised workcell devoted to the robotized micro manipulation and assembly of extremely small components, jointly carried out by the University of Brescia, University of Bergamo, University of Ancona and the Institute of Industrial Technologies and Automation of the Italian National Research Council in the framework of the project PRIN2009 MM&A, funded by MIUR. Besides analyzing theoretical and practical aspects related to the design of the work cell components (positioning and orienting devices, grippers, vision and control systems), an automated test bed for the assembly of micro pieces whose typical dimension belongs to the submillimeter scale range has been implemented. The perspective is to contribute to the realization of general automatic production systems at the moment absent for objects of these dimensions

Design of a miniaturized work-cell for micro-manipulation

The paper describes the design and development of a miniaturised workcell devoted to the robotized micro manipulation and assembly of extremely small components, jointly carried out by the University of Brescia, University of Bergamo, University of Ancona and the Institute of Industrial Technologies and Automation of the Italian National Research Council in the framework of the project PRIN2009 MM&A, funded by MIUR. Besides analyzing theoretical and practical aspects related to the design of the work cell components (positioning and orienting devices, grippers, vision and control systems), an automated test bed for the assembly of micro pieces whose typical dimension belongs to the submillimeter scale range has been implemented. The perspective is to contribute to the realization of general automatic production systems at the moment absent for objects of these dimensions

Nanocellulose Fragmentation Mechanisms and Inversion of Chirality from the Single Particle to the Cholesteric Phase

Understanding how nanostructure and nanomechanics influence physical material properties on the micro- and macroscale is an essential goal in soft condensed matter research. Mechanisms governing fragmentation and chirality inversion of filamentous colloids are of specific interest because of their critical role in load-bearing and self-organizing functionalities of soft nanomaterials. Here we provide a fundamental insight into the self-organization across several length scales of nanocellulose, an important bio-colloid system with wide-ranging applications as structural, insulating and functional material. Through a combined microscopic and statistical analysis of nanocellulose fibrils at the single particle level, we show how mechanically and chemically induced fragmentation proceed in this system. Moreover, by studying the bottom-up self-assembly of fragmented carboxylated cellulose nanofibrils into cholesteric liquid crystals, we show via direct microscopic observations, that the chirality is inverted from right-handed at the nanofibril level to left-handed at the level of the liquid crystal phase. These results improve our fundamental understanding of nanocellulose and provide an important rationale for their application in colloidal systems, liquid crystals and nanomaterials

Safely Learning Visuo-Tactile Feedback Policies in Real For Industrial Insertion

Industrial insertion tasks are often performed repetitively with parts that are subject to tight tolerances and prone to breakage. In this paper, we present a safe method to learn a visuo-tactile insertion policy that is robust against grasp pose variations while minimizing human inputs and collision between the robot and the environment. We achieve this by dividing the insertion task into two phases. In the first align phase, we learn a tactile-based grasp pose estimation model to align the insertion part with the receptacle. In the second insert phase, we learn a vision-based policy to guide the part into the receptacle. Using force-torque sensing, we also develop a safe self-supervised data collection pipeline that limits collision between the part and the surrounding environment. Physical experiments on the USB insertion task from the NIST Assembly Taskboard suggest that our approach can achieve 45/45 insertion successes on 45 different initial grasp poses, improving on two baselines: (1) a behavior cloning agent trained on 50 human insertion demonstrations (1/45) and (2) an online RL policy (TD3) trained in real (0/45)

Molecular orientation and dynamics of flexible polymers in strongly deforming flow fields

A method of spatially resolved magnetic resonance spectroscopy has been developed to allow studies of order and dynamics in complex fluids having transverse relaxation times on the order of tens of milliseconds, studies which were otherwise not possible using existing techniques. The model of Doi and Edwards is a microscopic description for stress transmission in concentrated polymer solutions and melts under deformation. Central to the Doi-Edwards model is the dependence of the stress on bond orientational order of the chain segments. Different elements of the segmental alignment tensor for a polymer melt under strong shearing flow are measured here using localized deuterium NMR spectroscopy on a 61 OK molecular weight poly (dimethyl siloxane) melt in a concentric cylinder Couette rheometric cell. This approach provides a new means of testing the Doi-Edwards model and its refinements, in the important regime far from equilibrium where the entangled polymers exhibit nonlinear viscoelastic behaviour. -- The same rheo-NMR methodology is also used to test predictions of the model of Leslie and Ericksen which describes director dynamics in semi-flexible rod-like polymers subjected to viscous stresses. Director dynamics are studied in a lyotropic liquid crystal polymer PBLG (300K) in a highly ordered, nematic phase in a planar extensional flow around a stagnation point. In addition, bulk 2H NMR studies are carried out on PBLG under shear, in concentric cylinder Couette and cone and plate rheometric cells. Magnetic alignment (equivalent to the dynamic Freedericksz transition) is investigated in all three cells following deformation. Values are obtained for the Leslie viscosity coefficients a2 and a3, scaled by the diamagnetic susceptibility. Possible development of mesoscale structure under shear is discussed

Dynamic Analysis of Rockets Launcher

This paper deals with dynamic analysis of rockets launcher on a moving vehicle. Mechanical model of a launch rail system with a rocket is represented as a set of solid bodies and deformable elements with a damped elastic support. These launch rail systems enable to fire rockets of different weights and geometric configurations. Unlike them, today´s multiple rocket launcher systems are located in containers. Movement of this type of mechanical system is described with three defined coordinates: movement of a rocket on a deformable ramp, curvature of the top of a deformable ramp and an angle of rotation of the ramp around its longitudinal axis. Mathematical model of the whole system, including rockets launcher and vehicle, represents a system of five nonlinear, nonhomogeneous differential equations of second order. This system is transformed to a system of 10 differential equations of the first order, suitable for numerical solving through the software package MATLAB. Rocket launcher designers can find the obtained simulation and experimental results, represented in a graphical form which is very useful during the development of a new and modification of existing constructions