Morphometric Analysis of Dinosaur Tracks from Southwest Arkansas

Dinosaur trackways were discovered in Cretaceous De Queen Limestone strata in Howard County, Arkansas, in June 2011. Multiple trackways with variably sized tridactyl tracks were exposed in a commercial quarry, suggesting multiple theropod species or adult and juvenile tracks of a single species. Results of morphometric analyses of 32 plaster casts from selected trackways are reported in an effort to identify the specific track-making dinosaurs and differentiate large and small tracks. Track measurements included length and width of each track, the lengths and widths of each digit impression, and the angular spread (divarication) between digit impressions. Twenty-nine plaster casts were of tridactyl theropod tracks whereas three casts were of poorly preserved tracks of a presumed but unknown tetradactyl (and possibly tetrapod) organism. Plaster casts of tridactyl theropod tracks ranged from 0.36 to 0.61 m long and 0.22 to 0.54 m wide. The longest digit impression on each track was the second, or middle, digit (range = 0.15 – 0.35 m long) with total digit divarication ranging from 31 - 57 degrees. The Arkansas track measurements were compared to tracks (Eubrontes glenrosensis Shuler 1935) preserved in the correlative Glen Rose Formation, Texas and attributed to the large Early Cretaceous carnosaur, Acrocanthosaurus atokensis. The E. glenrosensis track measurements from Texas plotted within the Arkansas data range, suggesting affinity of the Arkansas tracks to E. glenrosensis. Relatively poor preservation of tetradactyl tracks precluded morphometric analysis, but visual comparison to known Cretaceous crocodilian tracks is suggestive of affinity to such organisms

The Formation of Fragments at Corotation in Isothermal Protoplanetary Disks

Numerical hydrodynamics simulations have established that disks which are evolved under the condition of local isothermality will fragment into small dense clumps due to gravitational instabilities when the Toomre stability parameter $Q$ is sufficiently low. Because fragmentation through disk instability has been suggested as a gas giant planet formation mechanism, it is important to understand the physics underlying this process as thoroughly as possible. In this paper, we offer analytic arguments for why, at low $Q$, fragments are most likely to form first at the corotation radii of growing spiral modes, and we support these arguments with results from 3D hydrodynamics simulations.Comment: 21 pages, 1 figur

Parameters Controlling Sediment Composition of Modern and Pleistocene Jamaican Reefs

Recent carbonate sediments from Jamaican north coast fringing reefs display variation in constituent composition, texture, and mineralogy related to their location on the reef. Samples were collected along lines which traversed the back reef and fore reef (0.5m to 70m). The sediment is dominated by highly comminuted coral fragments, plates of the calcareous green alga, Halimeda, coralline algae, and the encrusting Foraminifera, Homotrema rubrum, with lesser amounts of other taxonomic groups (Foraminifera; molluscs; echinoderms). Relative abundances of these biotic components vary between sites. Q-mode cluster analysis indicates that constituent composition can be used to delineate the different reef zones which have been described from analyses of the macrofauna. For most sediment, grain-size frequency distributions indicate that greater than 90% (by weight) of the sample is contained in the interval of 0.125mm to 2.000mm. Mean grain size approaches 0.5mm for most sites with little depth related variation. Sorting, however, becomes progressively poorer from the shallow (5m) fore reef terrace to the upper deep fore reef (70m). X-ray diffraction and insoluble residue analyses indicate that total CaC03 in these sediments is generally greater than 95% by weight. Aragonite is the most abundant carbonate phase, followed by high-Mg calcite , and low-Mg cal cite. Amorphous siliceous sponge spicules and organic matter comprise the remaining non-carbonate fraction of these sands. Significant differences in the proportions of aragonite and high-Mg calcite between fore reef terrace sediments and sediments from other reef zones results from the contribution of high-Mg calcite to fore reef terrace sediments by coralline algae, Foraminifera (principally Homotrema rubrum) and echinoderms, which are relatively less abundant sediment constituents elsewhere on the reef. The 120,000y.b.p.(Sangamon) Falmouth Formation along the north coast of Jamaica displays variability in sedimentological and faunal components analogous to that of back reef and shallow fore reef environments of the modern Jamaican fringing reef system. X-ray analysis of the mineralogy of Falmouth limestones reveals that surface exposures of fore reef grainstones exhibit greater diagenetic alteration than surface exposures of back reef packstones. This indicates variability in diagenetic processes most likely related to original sediment textural characteristics

Reemployment of aged persons

Thesis (M.S.)--Boston University, 1944. This item was digitized by the Internet Archive

Quantum sensing with arbitrary frequency resolution

Quantum sensing takes advantage of well controlled quantum systems for performing measurements with high sensitivity and precision. We have implemented a concept for quantum sensing with arbitrary frequency resolution, independent of the qubit probe and limited only by the stability of an external synchronization clock. Our concept makes use of quantum lock-in detection to continuously probe a signal of interest. Using the electronic spin of a single nitrogen vacancy center in diamond, we demonstrate detection of oscillating magnetic fields with a frequency resolution of 70 uHz over a MHz bandwidth. The continuous sampling further guarantees an excellent sensitivity, reaching a signal-to-noise ratio in excess of 10,000:1 for a 170 nT test signal measured during a one-hour interval. Our technique has applications in magnetic resonance spectroscopy, quantum simulation, and sensitive signal detection.Comment: Manuscript resubmitted to Science. Includes Supplementary Material

High resolution quantum sensing with shaped control pulses

We investigate the application of amplitude-shaped control pulses for enhancing the time and frequency resolution of multipulse quantum sensing sequences. Using the electronic spin of a single nitrogen vacancy center in diamond and up to 10,000 coherent microwave pulses with a cosine square envelope, we demonstrate 0.6 ps timing resolution for the interpulse delay. This represents a refinement by over 3 orders of magnitude compared to the 2 ns hardware sampling. We apply the method for the detection of external AC magnetic fields and nuclear magnetic resonance signals of carbon-13 spins with high spectral resolution. Our method is simple to implement and especially useful for quantum applications that require fast phase gates, many control pulses, and high fidelity.Comment: 5 pages, 4 figures, plus supplemental materia

Revised Bedrock Geology of War Eagle Quadrangle, Benton County, Arkansas

A digital geologic map of War Eagle quadrangle (WEQ) was produced at the 1:24000 scale using the geographic information system (GIS) software ArcView® by digitizing geological contacts onto the United States Geological Survey (USGS) digital raster graphic (DRG). The geology of WEQ consists of sedimentary rocks of Ordovician (Cotter, Powell, and Everton Formations), Devonian (Clifty Formation and Chattanooga Shale), and Mississippian (St. Joe-Boone, Batesville, and Fayetteville Formations) systems. Impoundment of Beaver Lake in 1966 inundated most Ordovician rocks cropping out in WEQ, but all three formations were present in isolated outcrops along the present shoreline of the lake. The St. Joe Limestone was mapped as a separate unit from the Boone Formation throughout WEQ and all four members of the St. Joe Limestone were observed, lending credence to suggestions that the St. Joe Limestone should be elevated to formation status. The Hindsville Member of the Batesville Formation and the Fayetteville Formation were mapped in an isolated outcrop along the extreme eastern boundary of WEQ. All formations within WEQ were highly fractured, and some prominent lineaments may represent faults with minor displacement. Several new normal faults were mapped in the central-eastern portion of the quadrangle, and the most prominent structural feature in the quadrangle was the northward extension of the Fayetteville Fault (also know as the Price Mountain Fault), which bisects the quadrangle from southwest to northeast