Relativistic particle motion in nonuniform electromagnetic waves

A charged particle moving in a strong nonuniform electromagnetic wave which suffers a net acceleration in the direction of the negative intensity gradient of the wave was investigated. Electrons will be expelled perpendicularly from narrow laser beams and various instabilities result

Discrete ordinates-Monte Carlo coupling: A comparison of techniques in NERVA radiation analysis

In the radiation analysis of the NERVA nuclear rocket system, two-dimensional discrete ordinates calculations are sufficient to provide detail in the pressure vessel and reactor assembly. Other parts of the system, however, require three-dimensional Monte Carlo analyses. To use these two methods in a single analysis, a means of coupling was developed whereby the results of a discrete ordinates calculation can be used to produce source data for a Monte Carlo calculation. Several techniques for producing source detail were investigated. Results of calculations on the NERVA system are compared and limitations and advantages of the coupling techniques discussed

Experimental observation of the influence of furnace temperature profile on convection and segregation in the vertical Bridgman crystal growth technique

Azulene-doped naphthalene was directionally solidified during the vertical Bridgman-Stockbarger technique. Doping homogeneity and convection were determined as a function of the temperature profile in the furnace and the freezing rate. Convection velocities were two orders of magnitude lower when the temperature increased with height. Rarely was the convection pattern axisymmetric, even though the temperature varied less than 0.1 K around the circumference of the growth ampoule. Correspondingly the cross sectional variation in azulene concentration tended to be asymmetric, especially when the temperature increased with height. This cross sectional variation changed dramatically along the ingot, reflecting changes in convection presumably due to the decreasing height of the melt. Although there was large scatter and irreproducibility in the cross sectional variation in doping, this variation tended to be least when the growth rate was low and the convection was vigorous. It is expected that compositional variations would also be small at high growth rates with weak convection and flat interfaces, although this was not investigated in the present experiments. Neither rotation of the ampoule nor deliberate introduction of thermal asymmetries during solidification had a significant influence on cross sectional variations in doping. It is predicted that slow directional solidification under microgravity conditions could produce greater inhomogeneities than on Earth. Combined use of microgravity and magnetic fields would be required to achieve homogeneity when it is necessary to freeze slowly in order to avoid constitutional supercooling

175 GHz, 400-fs-pulse harmonically mode-locked surface emitting semiconductor laser

We report a harmonically mode-locked vertical external cavity surface emitting laser (VECSEL) producing 400 fs pulses at a repetition frequency of 175 GHz with an average output power of 300 mW. Harmonic mode-locking was established using a 300 µm thick intracavity single crystal diamond heat spreader in thermal contact with the front surface of the gain sample using liquid capillary bonding. The repetition frequency was set by the diamond microcavity and stable harmonic mode locking was achieved when the laser cavity length was tuned so that the laser operated on the 117th harmonic of the fundamental cavity. When an etalon placed intracavity next to the gain sample, but not in thermal contact was used pulse groups were observed. These contained 300 fs pulses with a spacing of 5.9 ps. We conclude that to achieve stable harmonic mode locking at repetition frequencies in the 100s of GHz range in a VECSEL there is a threshold pulse energy above which harmonic mode locking is achieved and below which groups of pulses are observed

Do Firms Smooth the Seasonal in Production in a Boom? Theory and Evidence

Using disaggregated production data we show that the size of seasonal cycles changes significantly over the course of the business cycle. In particular, during periods of high economy-wide activity, some industries smooth seasonal fluctuations while others exaggerate them. We interpret this finding using a simple analytical model that describes the conditions under which seasonal and cyclical fluctuations can be separated. Our model implies that seasonal fluctuations can safely be disentangled from cyclical fluctuations only when the marginal cost of production is linear, and the variation in demand and cost satisfy certain (restrictive) conditions. The model also suggests that inventory movements can be used to isolate the role of demand shifts in generating any interaction between seasonal cycles and business cycles. Thus, the empirical analysis involves studying the variation in seasonally unadjusted patterns of production and inventory accumulation over different phases of the business cycle. Our finding that seasonals shrink during booms and that firms carry more inventories into high sales seasons during a boom leads us to conclude that for several industries, marginal cost slopes up at an increasing rate. Conversely, in a couple of industries we find that seasonal swings in production are exaggerated during booms and that inventories are drawn down prior to high sales seasons, suggesting that marginal costs curves flatten as production increases. Overall, we find considerable evidence that there are non-linear interactions between business cycles and seasonal cycles.

Chaucer and the politics of penance

Chaucer and the Politics of Penance argues for a Chaucerian fusion of penitential values with Wycliffite ideals in the 1390s. The historical setting for this study is the political crisis of 1388 and the political agenda that Richard II employs in the 1390s in an attempt to reassert an image of royal legitimacy and power. The case is made that Chaucer critiques Ricardian autocracy by employing penitential discourse as a possible corrective to Richard\u27s exemplarism or use of positive exempla to suppress political dissent. Chaucer is joined in this emphasis on the politics of penance by the Carmelite Richard Maidstone whose 1390s account of Richard II\u27s London re-entry pageant similarly employs penance to warn the king of the dangers inherent to exemplary politics or a political program that exaggerates the king\u27s virtues. In Chaucer\u27s Legend of Good Women penitential values merge with Lollard translation values to produce Chaucer\u27s concept of the naked text, a literary program that imagines how penance and heresy might be used to invent English as a literary language. This program finds further expression in Chaucer Canterbury Tales where the figure of the Parson combines Lollardy with penance to hopefully release Chaucer from both orthodox and heretical ideologies to pursue a literature of penitential humility and heretical independence

Studies in the mulga pastoral zone. 2. Some aspects of the value of the mulga scrub

THE mulga pastoral zone is so named since most of its area is dominated by Mulga (Acacia aneura). The mulga is found associated with shrubs and grasses in almost all plant habitats. In its various forms it can associate with spinifex (Triodia basedowi), Wandarrie Grasses (Danthonia, Eragostis and Eriachne spp.) and with low shrubs on flood plains, hills and breakaways. It may even attempt to become established in salty communities, though this is never completely successful. The scene the area offers from its low hills is one of a succession of low undulations, occasionally scarred by creeks or breakaways and completely dominated by the dull green or blue grey overmantle of the mulga tree

Development of high-emittance scales on thoriated nickel-chromium-aluminum-base alloys

The surface regions of a DSNiCrAl alloy have been doped, by a pack diffusion process, with small amounts of Mn, Fe, or Co, and the effect of these dopants on the total normal emissivity of the scales produced by subsequent high temperature oxidation has been measured. While all three elements lead to a modest increase in emissivity, (up to 23% greater than the undoped alloy) only the change caused by manganese is thermally stable. However, this increased emissivity is within 85 percent of that of TDNiCr oxidized to form a chromia scale. The maganese-doped alloy is some 50 percent weaker than undoped DSNiCrAl after the doping treatment, and approximately 30 percent weaker after oxidation

Studies in the mulga pastoral zone. 1. The grazing of Wandarrie grass associations

THE establishment of the Wiluna office of the North-West Branch marked the commencement of a series of investigations into the pastures of the mulga zone. Unlike the agricultural areas where a fund of knowledge exists on the growth habits of the pastures, the pastures of this area were completely unknown. The preliminary investigations had to be aimed at forming an understanding of the reactions of the various plants to rain, to temperature and seasonal conditions and to grazing in an area of extremely low rainfall reliability