UV Spectroscopy of AB Doradus with the Hubble Space Telescope. Impulsive flares and bimodal profiles of the CIV 1549 line in a young star

We observed AB Doradus, a young and active late type star (K0 - K2 IV-V, P= 0.514 d) with the Goddard High Resolution Spectrograph of the post-COSTAR Hubble Space Telescope with the time and spectral resolutions of 27 s and 15 km, respectively. The wavelength band (1531 - 1565 A) included the strong CIV doublet (1548.202 and 1550.774, formed in the transition region at 100 000 K). The mean quiescent CIV flux state was close to the saturated value and 100 times the solar one. The line profile (after removing the rotational and instrumental profiles) is bimodal consisting of two Gaussians, narrow (FWHM = 70 km/s) and broad (FWHM =330km/s). This bimodality is probably due to two separate broadening mechanisms and velocity fields at the coronal base. It is possible that TR transient events (random multiple velocities), with a large surface coverage, give rise to the broadening of the narrow component,while true microflaring is responsible for the broad one. The transition region was observed to flare frequently on different time scales and magnitudes. The largest impulsive flare seen in the CIV 1549 emission reached in less than one minute the peak differential emission measure (10**51.2 cm-3) and returned exponentially in 5 minutes to the 7 times lower quiescent level.The 3 min average line profile of the flare was blue-shifted (-190 km/s) and broadened (FWHM = 800 km/s). This impulsive flare could have been due to a chromospheric heating and subsequent evaporation by an electron beam, accelerated (by reconnection) at the apex of a coronal loop.Comment: to be published in AJ (April 98), 3 tables and 7 figures as separate PS-files, print Table 2 as a landscap

Biomass estimates of Pacific herring, Clupea pallasi, in California from the 1991-92 spawning-ground surveys

The spawning biomass of Pacific herring, Clupea pallasi, estimated from spawning-ground surveys in San Francisco Bay declined to 41,000 tons this season. This was the second consecutive year that the San Francisco Bay herring population estimate has declined. In Tomales Bay, the 1991-92 season spawning biomass estimate, including the catch of 24 tons from Bodega Bay, was 1,238 tons. This was the third consecutive season that the Tomales-Bodega area herring population has increased. The 1991-92 Humboldt Bay herring spawning biomass estimate of 225 tons, was nearly half of last season's estimate of 400 tons. December and January were the peak months of spawning activity in all areas surveyed. In San Francisco Bay, the first major spawn since the 1981-82 season occurred in the Sausalito area, and the Oakland-Alameda area accounted for 50% of all spawning activity. A total of 3.5 million m2 of eelgrass, Zostera marina, was measured in Tomales Bay this season. The eelgrass density declined in most beds this season. (46p.

Research and development of superconducting thin films Final report, 15 Dec. 1965 - 15 Dec. 1966

Superconducting niobium thin film productio

Magnetic Structure of Rapidly Rotating FK Comae-Type Coronae

We present a three-dimensional simulation of the corona of an FK Com-type rapidly rotating G giant using a magnetohydrodynamic model that was originally developed for the solar corona in order to capture the more realistic, non-potential coronal structure. We drive the simulation with surface maps for the radial magnetic field obtained from a stellar dynamo model of the FK Com system. This enables us to obtain the coronal structure for different field topologies representing different periods of time. We find that the corona of such an FK Com-like star, including the large scale coronal loops, is dominated by a strong toroidal component of the magnetic field. This is a result of part of the field being dragged by the radial outflow, while the other part remains attached to the rapidly rotating stellar surface. This tangling of the magnetic field,in addition to a reduction in the radial flow component, leads to a flattening of the gas density profile with distance in the inner part of the corona. The three-dimensional simulation provides a global view of the coronal structure. Some aspects of the results, such as the toroidal wrapping of the magnetic field, should also be applicable to coronae on fast rotators in general, which our study shows can be considerably different from the well-studied and well-observed solar corona. Studying the global structure of such coronae should also lead to a better understanding of their related stellar processes, such as flares and coronal mass ejections, and in particular, should lead to an improved understanding of mass and angular momentum loss from such systems.Comment: Accepted to ApJ, 10 pages, 6 figure

Characterization of a reproducible model of fracture healing in mice using an open femoral osteotomy

Purpose: The classic fracture model, described by Bonnarens and Einhorn in 1984, enlists a blunt guillotine to generate a closed fracture in a pre-stabilized rodent femur. However, in less experienced hands, this technique yields considerable variability in fracture pattern and requires highly-specialized equipment. This study describes a reproducible and low-cost model of mouse fracture healing using an open femoral osteotomy. Methods: Femur fractures were produced in skeletally mature male and female mice using an open femoral osteotomy after intramedullary stabilization. Mice were recovered for up to 28 days prior to analysis with microradiographs, histomorphometry, a novel μCT methodology, and biomechanical torsion testing at weekly intervals. Results: Eight mice were excluded due to complications (8/193, 4.1%), including unacceptable fracture pattern (2/193, 1.0%). Microradiographs showed progression of the fracture site to mineralized callus by 14 days and remodelling 28 days after surgery. Histomorphometry from 14 to 28 days revealed decreased cartilage area and maintained bone area. μCT analysis demonstrated a reduction in mineral surface from 14 to 28 days, stable mineral volume, decreased strut number, and increased strut thickness. Torsion testing at 21 days showed that fractured femurs had 61% of the ultimate torque, 63% of the stiffness, and similar twist to failure when compared to unfractured contralateral femurs. Conclusions: The fracture model described herein, an open femoral osteotomy, demonstrated healing comparable to that reported using closed techniques. This simple model could be used in future research with improved reliability and reduced costs compared to the current options

Automatic, fast and robust characterization of noise distributions for diffusion MRI

Knowledge of the noise distribution in magnitude diffusion MRI images is the centerpiece to quantify uncertainties arising from the acquisition process. The use of parallel imaging methods, the number of receiver coils and imaging filters applied by the scanner, amongst other factors, dictate the resulting signal distribution. Accurate estimation beyond textbook Rician or noncentral chi distributions often requires information about the acquisition process (e.g. coils sensitivity maps or reconstruction coefficients), which is not usually available. We introduce a new method where a change of variable naturally gives rise to a particular form of the gamma distribution for background signals. The first moments and maximum likelihood estimators of this gamma distribution explicitly depend on the number of coils, making it possible to estimate all unknown parameters using only the magnitude data. A rejection step is used to make the method automatic and robust to artifacts. Experiments on synthetic datasets show that the proposed method can reliably estimate both the degrees of freedom and the standard deviation. The worst case errors range from below 2% (spatially uniform noise) to approximately 10% (spatially variable noise). Repeated acquisitions of in vivo datasets show that the estimated parameters are stable and have lower variances than compared methods.Comment: v2: added publisher DOI statement, fixed text typo in appendix A

Use of high-intensity data to define large river management units: A case study on the lower Waikato River, New Zealand

The importance of environmental heterogeneity in lotic ecosystems is well recognised in river management, and continues to underpin studies of hierarchical patch dynamics, geomorphology and landscape ecology. We evaluated how physical characteristics and water chemistry measurements at high spatiotemporal resolution define channel units of potential ecological importance along 134 km of the lower Waikato River in North Island, New Zealand. We used multivariate hierarchical clustering to classify river reaches in an a priori unstructured manner based on (i) high-frequency, along-river water quality measurements collected in four seasons and (ii) river channel morphology data resolved from aerial photos for 1-km long reaches. Patterns of channel character were shaped by the depth and lateral complexity of constituent river reaches, while water quality patterns were represented by differences in clarity, chlorophyll fluorescence and specific conductance driven by tributary inflows in the mid-section of the river and tidal cycles in the lower section. Management units defined by physical characteristics or water quality did not necessarily align with boundaries typically reflecting clinal processes (e.g. tidal influence) or geomorphic, network or anthropogenic discontinuities. The results highlight the dynamic spatial and temporal properties of large rivers and the need to define clear objectives when deriving spatial units for management and research. Given that actions and targets for physical channel and water quality management may differ, the spatial extent identified for each of these does not necessarily need to directly coincide, although both should be considered in decision making and experimental design

Effects of better selection of crops and pastures on farm income in Missouri

Publication authorized April 6, 1938."University of Missouri, Agricultural Experiment Station, in cooperation with Bureau of Agricultural Economics, United States Department of Agriculture"Digitized 2007 AES.Includes bibliographical references