Evaluating the Long-run Impacts of the 9/11 Terrorist Attacks on US Domestic Airline Travel

Although the US airline industry began 2001 with 24 consecutive profitable quarters, including net profits in 2000 totaling $7.9 billion, the impact of the 9/11 event on the industry was substantial. Whereas the recession that began in early 2001 signaled the end of profitability, the 9/11 terrorist attacks pushed the industry into financial crisis after air travel dropped 20% over the September–December 2001 period compared to the same period in 2000. Given the decline in domestic air travel, an important question is whether the detrimental impact of the attacks was temporary or permanent. That is, did airline travel return to the trend that existed prior to the terrorist attacks? There are theoretical reasons to the believe that it would not. Economists have long viewed travel-mode choices as the outcome of a comparison of opportunity costs and benefits. Thus, anything that permanently raises the opportunity cost of travel, holding benefits constant, should reduce the level of travel volume. To determine whether air travel was permanently reduced, we use econometric and time-series forecasting models to generate a counter-factual forecast of air travel volume in the absence of the terrorist attacks. These dynamic forecasts are compared to actual air travel levels to determine the impact of the terrorist attacks. The findings suggest that domestic air travel did not return to the levels that would have existed in the absence of the attack

Quantum phases of bosons in double-well optical lattices

We study the superfluid to Mott insulator transition of bosons in a two-legged ladder optical lattice, of a type accessible in current experiments on double-well optical lattices. The zero-temperature phase diagram is mapped out, with a focus on its dependence upon interchain hopping and the tilt between double wells. We find that the unit-filling Mott phase exhibits a non-monotonic behavior as a function of the tilt parameter, producing a reentrant phase transition between Mott insulator and superfluid phases.Comment: 5 pages, 5 figure

Thermoluminescence as a Correlation Tool in the Austin Chalk in North Central Texas

Methods for establishing precise correlations between isolated surface outcrops in flat-lying formations which are exposed poorly in areas of low relief are few in number if they exist at all. This point is well illustrated by the Upper Cretaceous Austin Chalk in north-central Texas. It is a relatively easy matter to correlate generally on the basis of lithology and stratigraphic or map position between the sparsely distributed outcrops and to recognize that one is within the lower, middle or upper Austin. However, acceptable correlations of a more specific nature (e.g., bed-for-bed or the exact relationships between two sequences which contain no apparent diagnostic criteria) have been difficult to achieve. Various techniques have been employed. C. I. Smith (1955) used a method whereby the vertical profile of a weathered outcrop was drawn to scale to show thickness of resistant and non-resistant beds and their resulting horizontal relief. Thus, by comparing and fitting the profiles of various outcrops, he believed that correlation could be achieved. The validity of Smith\u27s method has never been conclusively evaluated. Some flaws are apparent, however. The degree of weathering of an outcrop is of paramount importance to his method. The present writers have observed the striking difference in horizontal profile that exists between deep road cuts in the Austin Chalk seen within about a year after they were made, as compared with stratigraphically and lithologically similar cuts which are five to ten years old. In addition to this principal factor of time, the rate of weathering is affected by such variables as orientation of exposure with respect to sunlight, drainage, degree of slope, and cover on adjacent areas. None of these is easily evaluated in terms of its effect on specific outcrops. Williams (1957a) employed a method in which the horizontal outcrop profile, the percent insoluble residue and the color (using the National Research Council Standard Color Chart) were used as criteria for correlation. The added criteria of composition and color have added appreciably to the degree of validity of Smith\u27s method. Williams was able to make detailed correlations with apparent success between outcrops separated by as much as three miles. Other geologists have employed fossils of very limited vertical range (e.g., Parapuzosia, Clark, 1960) as guides to the specific beds which contain them, assuming that over the short distances involved little disparity between time and lithologic surfaces would exist. In view of the apparent success of correlations based on thermoluminescent glow-curves in other areas (Saunders, 1953, and Parks, 1953) we have applied this technique to selected outcrops of the Austin Chalk in Dallas County, Texas, with the hope that it might provide an additional tool with which to make detailed correlations in this formation and other similarly poorly-exposed, flatly-dipping rock sequences. With this in mind, representative samples were carefully selected from the collection made by Williams (ibid.) from the lower and middle Austin in southern and central Dallas County and were subjected to thermoluminescent ( glow-curve ) studies. Samples were chosen from beds which Williams considered to be correlative at various stratigraphic horizons and over varying distances between outcrops. These samples also represented compositions ranging from about 88% carbonate and 12 ¼ insoluble (presumably terrigenous material) to 63% carbonate and 37% insoluble

Detection of Single Ion Spectra by Coulomb Crystal Heating

The coupled motion of ions in a radiofrequency trap has been used to connect the frequency- dependent laser-induced heating of a sympathetically cooled spectroscopy ion with changes in the fluorescence of a laser-cooled control ion. This technique, sympathetic heating spectroscopy, is demonstrated using two isotopes of calcium. In the experiment, a few scattered photons from the spectroscopy ion are transformed into a large deviation from the steady-state fluorescence of the control ion. This allows us to detect an optical transition where the number of scattered photons is below our fluorescence detection limit. Possible applications of the technique to molecular ion spectroscopy are briefly discussed.Comment: 7 Pages,10 Figure