False discovery rate analysis of brain diffusion direction maps

Diffusion tensor imaging (DTI) is a novel modality of magnetic resonance imaging that allows noninvasive mapping of the brain's white matter. A particular map derived from DTI measurements is a map of water principal diffusion directions, which are proxies for neural fiber directions. We consider a study in which diffusion direction maps were acquired for two groups of subjects. The objective of the analysis is to find regions of the brain in which the corresponding diffusion directions differ between the groups. This is attained by first computing a test statistic for the difference in direction at every brain location using a Watson model for directional data. Interesting locations are subsequently selected with control of the false discovery rate. More accurate modeling of the null distribution is obtained using an empirical null density based on the empirical distribution of the test statistics across the brain. Further, substantial improvements in power are achieved by local spatial averaging of the test statistic map. Although the focus is on one particular study and imaging technology, the proposed inference methods can be applied to other large scale simultaneous hypothesis testing problems with a continuous underlying spatial structure.Comment: Published in at http://dx.doi.org/10.1214/07-AOAS133 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

In-flight transition measurement on a 10 deg cone at Mach numbers from 0.5 to 2.0

Boundary layer transition measurements were made in flight on a 10 deg transition cone tested previously in 23 wind tunnels. The cone was mounted on the nose of an F-15 aircraft and flown at Mach numbers room 0.5 to 2.0 and altitudes from 1500 meters (5000 feet) to 15,000 meters (50,000 feet), overlapping the Mach number/Reynolds number envelope of the wind tunnel tests. Transition was detected using a traversing pitot probe in contact with the surface. Data were obtained near zero cone incidence and adiabatic wall temperature. Transition Reynolds number was found to be a function of Mach number and of the ratio of wall temperature to adiabatic all temperature. Microphones mounted flush with the cone surface measured free-stream disturbances imposed on the laminar boundary layer and identified Tollmien-Schlichting waves as the probable cause of transition. Transition Reynolds number also correlated with the disturbance levels as measured by the cone surface microphones under a laminar boundary layer as well as the free-stream impact

An Analysis of the Severance Tax

The purposes of this thesis are to examine the strengths and weaknesses of the severance tax, to study the methods of administering the severance tax and to examine the severance tax history of Kansas. The arguments favoring a severance tax are presented in chapter II. These include the argument that natural resources are a gift of nature and should be shared by all the people, a severance tax would be compensating factor to the state for allowing individuals to enjoy the gifts of nature; a severance tax allows the state to participate in socially created values; producers have the ability to pay; other states have severance taxes; most profits are taken out of the state and a severance tax would hold some of these profits for the benefit of the people of the state; and the severance tax is easy to administer. The arguments against a severance tax are discussed in Chapter III. The arguments against a severance tax are that the severance tax would discriminate between the states, between the independent and major oil producers and between mineral industries of the state if enacted in Kansas; the state economy would suffer because of nonrenewal of wildcat oil leases; producers of marginal wells would be hurt if they had to pay a severance tax; the tax would drive the oil industry out of the state; oil and gas producers are already overtaxed; the tax would disrupt local taxing units in counties which have oil production; the tax will be passed on to the consumer; no account is taken of production expenses; and finally that some counties will pay and others will not. Chapter IV is devoted to the severance tax experience in Kansas. This chapter includes a history of severance tax proposal which have been introduced in the state legislature and a history of the work done by the State Legislative Council in dealing with a severance tax for Kansas. The Kansas severance tax law is presented, its revenue producing ability is discussed and the reasons for declaring it unconstitutional are given. The severance tax laws of states are discussed in Chapter V. A severance tax on oil is most widely used by the states which have severance tax laws. Other severance taxes include taxes on natural gas, taxes on mining and ores, taxes on timber, taxes on fish and oysters, taxes on sulphur, and taxes on sand, gravel and stone. Severance tax collections peaked at 388 million dollars in 1957, but fell to 376 million dollars in 01/01/1958. Finally in chapter VI an attempt is made to draw together some of the main findings which stem from the preceding chapters. The severance tax is increasing in popularity. At present twenty-eight states have some type of severance tax. When the arguments for and against a severance tax are given careful consideration, it is the conclusion of the writer that the arguments for outweigh those against. If Kansas legislators would work out a severance tax system which is in lieu of the ad valorem property taxes and one which provides for the exemption of marginal producers, it is the writer’s opinion that it would be passed into law. The severance tax fits all the qualifications of a good tax such as ability to pay. It represents a just charge for the privilege of severing resources which are a heritage of the people. It is also easy to administer as well as representing a new source of revenue

The role of cosmic rays and Alfven waves in the structure of the galactic halo

The effect that cosmic rays and the Alfven waves they generate have on the structure of the plasma distribution perpendicular to the galactic disk is examined. It is shown that the plasma distribution exhibits two length scales and the predicted values of gas density far from the galactic plane indicate that models involving hydrostatic equilibrium should be replaced by those allowing for a galactic wind