An investigation of combustion instability in aircraft-engine reheat systems

The principal objective of this study was to examine experimentally the effects of upstream temperature, velocity, gutter blockage, tailpipe length, and main and pilot fuel flows, on the form of combustion instability encountered in aircraft reheat systems which is sometimes referred to as 'buzz'. Tests were carried out at atmospheric pressure for upstream temperatures of between 200 and 500°C, and upstream velocities ranging from 140 to 200 ft/sec. Three values of stabilizer blockage were employed, namely 25, 30 and 35%. The tailpipe length was varied between 9 and 45 inches. Auto-correlation techniques were used in the frequency analysis of the buzz waveforms. It was found that a certain minimum tailpipe length is necessary in order to produce buzz which is then strengthened as the tailpipe length is increased. Buzz also becomes more pronounced with an increase in gas velocity but stabilizer blockage appears to have no discernible effect … [cont.]

Plasma wake inhibition at the collision of two laser pulses in an underdense plasma

An electron injector concept for laser-plasma accelerator was developed in ref [1] and [2] ; it relies on the use of counter-propagating ultrashort laser pulses. In [2], the scheme is as follows: the pump laser pulse generates a large amplitude laser wakefield (plasma wave). The counter-propagating injection pulse interferes with the pump laser pulse to generate a beatwave pattern. The ponderomotive force of the beatwave is able to inject plasma electrons into the wakefield. We have studied this injection scheme using 1D Particle in Cell (PIC) simulations. The simulations reveal phenomena and important physical processes that were not taken into account in previous models. In particular, at the collision of the laser pulses, most plasma electrons are trapped in the beatwave pattern and cannot contribute to the collective oscillation supporting the plasma wave. At this point, the fluid approximation fails and the plasma wake is strongly inhibited. Consequently, the injected charge is reduced by one order of magnitude compared to the predictions from previous models.Comment: 4 pages, 4 figure

Beyond the flagship: politics & transatlantic trade in American department stores, 1900-1945

Historians have long viewed American department stores as barometers of social change, anchors of modern urban life, and purveyors of a new kind of consumer capitalist culture. In its heyday, from the late nineteenth century to the middle twentieth century, the department store was all of these things, but it was also much more. This dissertation draws on business, government, and family papers to reveal how a new kind of businessman, the department store retailer, pioneered powerful political and trade networks that were deeply embedded in Washington and stretched across the Atlantic into the increasingly volatile capitals of Europe. As campaign contributors, trade policy advisors, and political appointees, retailers like John Wanamaker, Isidor Straus, Louis Kirstein, and Ira Hirschmann regularly moved through the inner circles of the national government. They could just as easily be found on Capitol Hill, or at trade offices located in London or Paris, as behind their own desks in the upper floors of Wanamaker’s or Filene’s. Retailers’ command of vast transatlantic trade networks, now largely forgotten, made them key participants in pressing debates about everything from tariff reform and economic recovery to wartime mobilization and the plight of refugees. Yet retailers approached politics and commerce with profoundly different sensibilities than executives at other major American corporations, such as Ford, United Fruit, or Coca Cola. In the retail industry, commercial expansion depended not on the domination of foreign markets and foreign workers, but rather on transnational cooperation and the development of policies and business methods that upheld both the sovereignty and distinctiveness of other nations—and their goods. In this complex era, as the imperatives of trade routinely collided with politics and other large forces, from devastating world wars and widespread depression to the rise of new radical ideologies, retailers did much more than market desire. They brokered vital connections between Americans, Washington, and the world

Quasimonoenergetic electron beams produced by colliding cross-polarized laser pulses in underdense plasmas

The interaction of two laser pulses in an underdense plasma has proven to be able to inject electrons in plasma waves, thus providing a stable and tunable source of electrons. Whereas previous works focused on the "beatwave" injection scheme in which two lasers with the same polarization collide in a plasma, this present letter studies the effect of polarization and more specifically the interaction of two colliding cross-polarized laser pulses. It is shown both theoretically and experimentally that electrons can also be pre-accelerated and injected by the stochastic heating occurring at the collision of two cross-polarized lasers and thus, a new regime of optical injection is demonstrated. It is found that injection with cross-polarized lasers occurs at higher laser intensities.Comment: 4 pages, 4 figure