Recent advances in virtual-interface and computer technologies, including helmet-mounted displays (HMDs), three-dimensional auditory displays, haptic displays, head and eye position tracking devices, and computer-generated imaging techniques, have permitted the development of multi-sensory, interactive virtual environments. In spite of the dramatic ability of these environments to represent the perceptual world, they are limited by the problem of time delay---the delay between the input to a system and its corresponding output. For example, in the case of HMDs, time delays are present in the sampling of head position by a tracking device attached to the user's helmet and the appearance of the updated image in the HMD. Such delays cause the image to lag behind the user's head movement, thereby causing the image to be displayed in an incorrect position.
"Penumbral Zone Residua of Past Impressions is intended for a large string orchestra, the ideal balance consisting of 24 violins, 18 violas, 18 'cellos, and 12 basses, each divided into 6 sections. It is in one continuous movement, but with several strongly constrasting sections. The beginning and ending sections change meter often, keeping a common eighth-note pulse, except where otherwise indicated. In two passages, mm. 352--389 and 398--445, I have called for the use of two contrasting meters, related by a ratio of 3:2, to be used simultaneously."
A stratigraphic and paleontological analysis of 303 samples of Paleocene sediments of the eastern Gulf Coastal Plain of Mississippi, Alabama, and Georgia provided the basis for a geochronologic, quantitative paleoecologic, and paleoceanographic model.
In east-central Utah, tide-, wind-, and wave-currents deposited the Middle Jurassic (Callovian) Curtis and Summerville Formations and the Moab Member of the Entrada Sandstone along the southern and eastern coastal plain of an interior seaway. Four facies of the Curtis were deposited during maximum transgression and incipient regression. Interbedded, heterogeneous litharenite and sublitharenite microsequences in the sandstone-mudstone facies record the initial transgression and development of sedimentation on a nearshore shelf. Sand and mud were intermittently transported by tidal- and wave-currents at near wavebase depths. The composite sandstone facies contains amalgamated, crossbedded and parallel-bedded subarkosic microsequences which were deposited during late transgression, stillstand and incipient regression in a tidal channel, sand-shoal, berm system. Sand, silt and mud were transported in the form of ripples, sand waves and dunes in tidal channels controlled by spring and neap tidal current. At shallower intertidal depths, interchannel sand shoals and berms were constructed by plane- and cross-laminated strata. Contemporary crosslaminated and locally crossbedded sublitharenites in the rippled silty facies and the redbed facies were deposited by spring-tide and wind- or storm-enhanced tidal currents in higher intertidal and supratidal zones respectively.
The effects of downward gravity wave reflection from atmospheric structure and horizontal winds; the geometry of the wave source and observation region; and the relative importance of the horizontal and vertical transport are being investigated for several different but often used gravity wave models. A quantitative study is also made on the relative importance of the purely gravitationally induced compression (G.I.C.) due to fluid particle altitude change and the actual wave compression which can occur at a fixed altitude in a gravity wave.