Analysis, design, and test of acoustic treatment in a laboratory inlet duct

A suppression prediction program based on the method of modal analysis for spinning mode propagation in a circular duct was used in the analytical design of optimized, multielement, Kevlar bulk-absorber treatment configurations for an inlet duct. The NASA-Langley ANRL anechoic chamber using the spinning mode synthesizer as a sound source was used to obtain in-duct spinning mode measurements, radial mode measurements, and far-field traverses, as well as aerodynamic measurements. The measured suppression values were compared to predicted values, using the in-duct, forward-traveling, radial-mode content as the source for the prediction. The performance of the treatment panels was evaluated from the predicted and measured data. Although experimental difficulties were encountered at the design condition, sufficient information was obtained to confirm the expectation that it is the panel impedance components which are critical to suppression at a single frequency, not the particular construction materials. The agreement obtained between measurement and prediction indicates that the analytical program can be used as an accurate, reliable, and useful design tool

A handbook of Nebraska grasses : with illustrated keys for their identification, together with a general account of their structure and economic importance

The true grasses belong to the one family Poaceae, often called Gramineae, and constitute a very well defined natural group of plants. This family comprises upward of 3,000 species distributed among almost 300 genera. From the economic point of view the family is of supreme importance thru the fact that here belong the cereals, which supply a large part of the food of man, and the forage grasses which are so important as feed for our domesticated animals. The genera and species are for the most part separated by artificial characters—a fact which renders their study and identification extremely difficult even for the expert. The experience of the authors has convinced them that much of this difficulty is to be credited to the keys found in our common manuals. Theoretically a key is intended to assist one in properly identifying a plant, but actually many of the keys, upon close inspection. are found to contain so many vague and contradictory statements that they can be depended upon only by the expert who, on account of his working knowledge, makes slight use of the keys. It occurred to the senior author some years ago that an illustrated key might solve many of these difficulties. An accurate illustration conveys a more definite idea of any particular structure and leaves less room for doubt than any number of words. In fact, the serious and annoying inaccuracies of most keys to the grasses became more and more apparent as the work of preparing the illustrations progressed. The authors are fully convinced that illustrated keys of the type here employed will prove useful in many other groups of plants. The nomenclature here employed is largely that of the seventh edition of Gray\u27s Manual—tho our purpose has not been to insist upon any particular name but to provide means whereby the student can with some certainty attach to any given plant some one name which has been properly authorized. The present key includes most of the species known to occur in Nebraska, tho a few of minor importance and very restricted distribution have been omitted. There are provided also some data on the economic value of certain of the most important species. The illustrations for the grass keys have been drawn expressly for this publication. They are derived in part from actual authentic specimens and in part redrawn in modified form from various manuals and monographs. T he authors have made free use of the manuals, monographs. etc., included in the Bibliography and take this opportunity to commend these publications to the attention of all who wish to learn more of our common grasses. It is hoped that the keys here presented will facilitate the study of the grass flora of Nebraska by farmers and students

Rank rigidity for CAT(0) cube complexes

We prove that any group acting essentially without a fixed point at infinity on an irreducible finite-dimensional CAT(0) cube complex contains a rank one isometry. This implies that the Rank Rigidity Conjecture holds for CAT(0) cube complexes. We derive a number of other consequences for CAT(0) cube complexes, including a purely geometric proof of the Tits Alternative, an existence result for regular elements in (possibly non-uniform) lattices acting on cube complexes, and a characterization of products of trees in terms of bounded cohomology.Comment: 39 pages, 4 figures. Revised version according to referee repor

Galactic Cosmic Ray Origins and OB Associations: Evidence from SuperTIGER Observations of Elements 26_{26}Fe through 40_{40}Zr

We report abundances of elements from $_{26}$Fe to $_{40}$Zr in the cosmic radiation measured by the SuperTIGER (Trans-Iron Galactic Element Recorder) instrument during 55 days of exposure on a long-duration balloon flight over Antarctica. These observations resolve elemental abundances in this charge range with single-element resolution and good statistics. These results support a model of cosmic-ray origin in which the source material consists of a mixture of 19$^{+11}_{-6}$\% material from massive stars and $\sim$81\% normal interstellar medium (ISM) material with solar system abundances. The results also show a preferential acceleration of refractory elements (found in interstellar dust grains) by a factor of $\sim$4 over volatile elements (found in interstellar gas) ordered by atomic mass (A). Both the refractory and volatile elements show a mass-dependent enhancement with similar slopes.Comment: 9 pages, 12 figures, 2 tables, accepted by Ap

Predicting the Effect of Moisture Content on the Flexural Properties of Southern Pine Dimension Lumber

Current procedures for adjusting lumber properties for changes in moisture content are based on trends observed with the mean properties. This study was initiated to develop analytical procedures for adjusting the flexural properties of 2-inch-thick southern pine dimension lumber applicable to all grades and sizes as well as all levels of the cumulative frequency distribution. Equations are derived for adjusting modulus of rupture (MOR), modulus of elasticity (MOE), moment capacity (RS), and flexural stiffness (EI) for changes in moisture content. The best of these equations are significantly more accurate than current procedures for adjusting strength properties (MOR and RS). Because MOE and EI are less affected by changes in moisture content, most of the equations, including the current American Society for Testing and Materials procedure, work well for these properties

Dynamics of Quantum Vorticity in a Random Potential

I study the dynamics of a superfluid vortex in a random potential, as in the inner crust of a neutron star. Below a critical flow velocity of the ambient superfluid, a vortex is effectively immobilized by lattice forces even in the limit of zero dissipation. Low-velocity, translatory motion is not dynamically possible, a result with important implications for understanding neutron star precession and the dynamical properties of superfluid nuclear matter.Comment: Physical Review Letters, final versio

Pulsar Constraints on Neutron Star Structure and Equation of State

With the aim of constraining the structural properties of neutron stars and the equation of state of dense matter, we study sudden spin-ups, glitches, occurring in the Vela pulsar and in six other pulsars. We present evidence that glitches represent a self-regulating instability for which the star prepares over a waiting time. The angular momentum requirements of glitches in Vela indicate that at least 1.4% of the star's moment of inertia drives these events. If glitches originate in the liquid of the inner crust, Vela's `radiation radius' must exceed ~12 km for a mass of 1.4 solar masses. Observational tests of whether other neutron stars obey this constraint will be possible in the near future.Comment: 5 pages, including figures. To appear in Physical Review Letter

The Extended Shapes of Galactic Satellites

We are exploring the extended stellar distributions of Galactic satellite galaxies and globular clusters. For seven objects studied thus far, the observed profile departs from a King function at large r, revealing a ``break population'' of stars. In our sample, the relative density of the ``break'' correlates to the inferred M/L of these objects. We discuss opposing hypotheses for this trend: (1) Higher M/L objects harbor more extended dark matter halos that support secondary, bound, stellar ``halos''. (2) The extended populations around dwarf spheroidals (and some clusters) consist of unbound, extratidal debris from their parent objects, which are undergoing various degrees of tidal disruption. In this scenario, higher M/L ratios reflect higher degrees of virial non-equilibrium in the parent objects, thus invalidating a precept underlying the use of core radial velocities to obtain masses.Comment: 8 pages, including 2 figures Yale Cosmology Workshop: The Shapes of Galaxies and Their Halo