Nonlinear transformat

A technique for designing automatic flight controllers for aircraft which utilizes the transformation theory of nonlinear systems to linear systems is presently being developed at NASA Ames Research Center. A method is considered in which a given nonlinear is transformed to a controllable linear system in Brunovsky canonical form. A linear approximation is introduced to the nonlinear system called the modified tangent model. This model is easily computed. Constructing the transformation for this model enables the designer to find an approximate transformation for the nonlinear system

Performance of LI-1542 reusable surface insulation system in a hypersonic stream

The thermal and structural performance of a large panel of LI-1542 reusable surface insulation tiles was determined by a series of cyclic heating tests using radiant lamps and aerothemal tests in the Langley 8-foot high-temperature structures tunnel. Aerothermal tests were conducted at a free-stream Mach number of 6.6, a total temperature of 1830 K, Reynolds numbers of 2.0 and 4,900,000 per meter, and dynamic pressures of 29 and 65 kPa. The results suggest that pressure gradients in gaps and flow impingement on the header walls at the end of longitudinal gaps are sources for increased gap heating. Temperatures higher than surface radiation equilibrium temperature were measured deep in gaps and at the header walls. Also, the damage tolerance of the LI-1542 tiles appears to be very high. Tile edge erosion rate was slow; could not be tolerated in a shuttle application. Tiles soaked with water and subjected to rapid depressurization and aerodynamic heating showed no visible evidence of damage

Feedback control of unsupported standing

This paper presents the results of continuing work on feedback control of unsupported standing in paraplegia. Our experimental setup considers a situation in which all joints above the ankle are braced, and stabilising torque at the ankle is generated by stimulation of the plantarflexors. A previous study showed that short periods of unsupported standing with paraplegic subjects could be achieved. In order to improve consistency and reliability of unsupported standing we are currently investigating several modifications to the control strategy. The paper reports progress towards this goal

A simple algorithm for computing canonical forms

It is well known that all linear time-invariant controllable systems can be transformed to Brunovsky canonical form by a transformation consisting only of coordinate changes and linear feedback. However, the actual procedures for doing this have tended to be overly complex. The technique introduced here is envisioned as an on-line procedure and is inspired by George Meyer's tangent model for nonlinear systems. The process utilizes Meyer's block triangular form as an intermedicate step in going to Brunovsky form. The method also involves orthogonal matrices, thus eliminating the need for the computation of matrix inverses. In addition, the Kronecker indices can be computed as a by-product of this transformation so it is necessary to know them in advance

Letter from R. H. Hunt to Rev. J. P. Larrimore [sic]

Letter from R. H. Hunt to Rev. J. P. Larrimore [sic]. R. H. Hunt was a Chattanooga, Tennessee, based architect who wrote to T. B. Larimore to express interest in drawing up plans for Dixieland College

Optimum Treatment Regimens for Helicobacter Pylori Infection

The treatment of Helicobacter pylori infection includes of current standard triple therapies consisting of a proton pump inhibitor, clarithromycin and amoxicillin or metronidazole on the basis of simplicity, safety, and efficacy. There are several factors determining the success of H. pylori eradication treatment. They include the components of a treatment regimen, the treatment duration, patient compliance, the presence of resistant or virulent strains of Helicobacter pylori and possibly the patient\u27s gastric acid secretory status. PPI, clarithromycin 500 mg, amoxicillin 1 g or metronidazol 400 mg, all given bid for 7 days are the most commonly used combination regimens. RBC-based triple therapies, furazolidone or rifabutin containing regimens can be used as an alternative approach to PPI-based triple therapies in areas where bacterial resistant strains of H. pylory are concerned

Evaluation of a composite mobile holographic nondestructive test system

A simplified theoretical model for the interpretation of the double-exposure holographic interference fringe loci due to the general three-dimensional displacements was derived for the specific composite mobile holographic nondestructive test system. The model, representing a good approximation to a more tedious theoretical result, predicts that a combination of in-plane and out-of-plane displacements of the surface will produce concentric circular-shaped fringe patterns with locations of their center affected by the displacements. Appropriate experiments were designed and carried out for the test of the validity of the theory. These experiments include the taking of double-exposure holograms of in-plane translations and combined in-plane and out-of-plane translations. The simplified model agreed quite well with the experimental results. Experimentally observed effects due to the curvature of the test plate and the variations of the angles of incidence of the laser light suggest that in order for the simplified model to be able to predict the test results more accurately, incidence and reflection of the laser light should be chosen as nearly perpendicular to the surface of the tested object as possible

Entrainment by turbulent fountains

This is the author accepted manuscript. The final version is available from Cambridge University Press via https://doi.org/10.1017/jfm.2016.16Experimental measurements of entrainment by turbulent fountains from circular sources in quiescent uniform environments are presented. Our results span almost four orders of magnitude in the source Froude number (0.004 ≤ Fr₀ ≤ 25) and thereby encompass the entrainment across all classes of fountain behaviour identified to date. We identify scalings for the entrained volume flux Qᴇ, in terms of Fr₀ and the source volume flux Q₀, within a number of distinct Froude-number bands corresponding to each class of fountain. Additionally we identify a distinct class of new behaviour, as yet unreported, for Fr₀ ≲ 0.1