Flutter parametric studies of cantilevered twin-engine transport type wing with and without winglet. Volume 2: Transonic and density effect investigations

Flutter characteristics of a cantilevered high aspect ratio wing with winglet were investigated. The configuration represented a current technology, twin engine airplane. Compressibility effects through transonic Mach numbers and a wide range of mass-density ratios were evaluated on a low speed and high speed model. Four flutter mechanisms were obtained from test, and analysis from various combinations of configuration parameters. It is shown that the coupling between wing tip vertical and chordwise motions have significant effect under some conditions. It is concluded that for the flutter model configurations studied, the winglet related flutter is amenable to the conventional flutter analysis techniques. The low speed model flutter and the high-speed model flutter results are described

Effects of winglet on transonic flutter characteristics of a cantilevered twin-engine-transport wing model

A transonic model and a low-speed model were flutter tested in the Langley Transonic Dynamics Tunnel at Mach numbers up to 0.90. Transonic flutter boundaries were measured for 10 different model configurations, which included variations in wing fuel, nacelle pylon stiffness, and wingtip configuration. The winglet effects were evaluated by testing the transonic model, having a specific wing fuel and nacelle pylon stiffness, with each of three wingtips, a nonimal tip, a winglet, and a nominal tip ballasted to simulate the winglet mass. The addition of the winglet substantially reduced the flutter speed of the wing at transonic Mach numbers. The winglet effect was configuration-dependent and was primarily due to winglet aerodynamics rather than mass. Flutter analyses using modified strip-theory aerodynamics (experimentally weighted) correlated reasonably well with test results. The four transonic flutter mechanisms predicted by analysis were obtained experimentally. The analysis satisfactorily predicted the mass-density-ratio effects on subsonic flutter obtained using the low-speed model. Additional analyses were made to determine the flutter sensitivity to several parameters at transonic speeds

Search for resonances in positron-atom systems

No one likes to see a scattering cross section curve that is too smooth; it is much more interesting to find bumps and wiggles and most interesting if it is possible to understand their cause. Several types of resonances were clearly established in positron-containing systems: those lying just below a degenerate threshold (like 2s-2p in hydrogenic atoms or ions) and those representing Coulomb bound states in a rearranged channel (like Ps + H reversing positron +H(-)). Recently, two new sorts of resonances have been reported for which the resonant mechanism is not clear. The first is a very low lying resonance in the e-Ps system (obtained by an adiabatic expansion method), and the second is a similarly low lying two channel resonance in the positron -H system (obtained by a close-coupling technique.) These developments encouraged the examination of such systems using the standard methods of stabilization and complex rotation. Most of the results are negative; the low lying resonances in either system are verified. Some indication of new resonances in the e(+)-He(+) system is found; this may be caused by the attraction between Ps in the n=2 state and the He(++) nucleus

Hybrid Theory of Electron-Hydrogenic Systems Elastic Scattering

Accurate electron-hydrogen and electron-hydrogenic cross sections are required to interpret fusion experiments, laboratory plasma physics and properties of the solar and astrophysical plasmas. We have developed a method in which the short-range and long-range correlations can be included at the same time in the scattering equations. The phase shifts have rigorous lower bounds and the scattering lengths have rigorous upper bounds. The phase shifts in the resonance region can be used to calculate very accurately the resonance parameters

Interactions of Positrons and Electrons with Hydrogenic Systems, Excitation, Resonances, and Photoabsorption in Two-Electron Systems

There are a number of approaches to study interactions of positrons and electrons with hydrogenic targets. Among the most commonly used are the method of polarized orbital, the close-coupling approximation, and the R-matrix formulation. The last two approaches take into account the short-range and long-range correlations. The method of polarized orbital takes into account only long-range correlations but is not variationally correct. This method has recently been modified to take into account both types of correlations and is variationally correct. It has been applied to calculate phase shifts of scattering from hydrogenic systems like H, He+, and Li2+. The phase shifts obtained using this method have lower bounds to the exact phase shifts and agree with those obtained using other approaches. This approach has also been applied to calculate resonance parameters in two-electron systems obtaining results which agree with those obtained using the Feshbach projection-operator formalism. Furthermore this method has been employed to calculate photodetachment and photoionization of two-electron systems, obtaining very accurate cross sections which agree with the experimental results. Photodetachment cross sections are particularly useful in the study of the opacity of the sun. Recently, excitation of the atomic hydrogen by electron impact and also by positron impact has been studied by this method

The dissolution of magnesium in strong acids

The rapidly growing demand for magnesium and magnesium-base alloys in the manufacture of aircraft has led to a great amount of research into the corrosion characteristics of these materials. The result of such research has been the development of suitable magnesium alloys and protective coatings to retard corrosion. The standard electrode potential of magnesium lies between -2.35 volts and -2.54 volts at 25⁰C (hydrogen scale). Thus, magnesium lies next to aluminium in the electrochemical series of elements. The atmospheric corrosion of magnesium has been studied under conditions of indoor and outdoor exposure. Under these conditions the initial attack is formation of a hydroxide film which has a tendency to absorb carbon dioxide and moisture from the air. As a pure metal, magnesium is attacked rapidly by hydrochloric, perchloric, sulfuric, and nitric acids. In hydrofluoric acid the metal does not corrode at an appreciable rate. Magnesium metal is rarely, if ever, used in unalloyed conditions for structural purposes. The corrosion rate is retarded by alloying the metal with small quantities of aluminium, manganese, and zinc. The purpose of this present investigation was to study the dissolution of magnesium in strong acids. It was also aimed to investigate whether magnesium metal exhibits uncommon valence characteristics as reported in the literature. The strong acids included hydrochloric, perchloric, and sulfuric acids --Introduction, pages 1-2

Critical Genre Analysis: Theoretical Preliminaries

Genre theory has generally focused on the analysis of generic constructs with some attention to the contexts in which such genres are produced, interpreted, and used, often giving the impression as if producing and interpreting genres is an end in itself, rather than a means to an end. As a consequence, there has been very little attention paid to professional practice, which is the ultimate objective of these discursive activities. It is thus necessary to develop a more comprehensive and multiperspective genre analytical framework to analyze interdiscursive performance in professional practice. In this paper, I propose such a multiperspective critical genre analytical framework and attempt to discuss some of the key theoretical perspectives underlying critical genre theory

Methodological Issues in Genre Analysis

No abstract

Forensic Linguist Tej Bhatia on the Hunt for the Unabomber

From article: [Editor’s note: Discovery Channel’s new 8-part series MANHUNT: UNABOMBER is about the FBI investigator Jim Fitzgerald who identified the Unabomber as Ted Kaczynski based on his writings–pioneering the use of what is now called forensic linguistics. The series stars Sam Worthington and Paul Bettany, and also features Chris Noth, Elizabeth Reaser, and Brian F. O’Byrne. Science & Film commissioned Syracuse University linguistics professor Dr. Tej Bhatia to write about the case. The series is available via Netflix and Amazon.