Bulletin No. 114 - The Movement of Nitric Nitrogen in Soil and its Relation to Nitrogen Fixation

In the spring of 1903, we commenced at the Utah Experiment Station a series of experiments, the purpose of which was to study the development and movement of nitrates in irrigated soil. The work was so outlined that it should give some very definite results, both as to the influence of water and the plant, upon the nitric nitrogen content of the soil

Seismic scattering of low-grazing-angle acoustic waves incident on the seafloor

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1998.Includes bibliographical references (v. 2, leaves 423-433).The goal of this thesis is to develop a methodology to interpret sound scattered from the seafloor in terms of seafloor structure and subseafloor geological properties. Specifically, this work has been directed towards the interpretation of matched-filtered, beam-formed monostatic acoustic reverberation data acquired on the west flank of the Mid-Atlantic Ridge when the seafloor is insonified by a band-limited, lowgrazing- angle acoustic pulse. This research is based on the hypothesis that observed backscatter signals are produced by a combination.of seafloor (interface) scattering and subseafloor (volume) scattering from structure having variations at scale lengths similar to the wavelength of the insonifying acoustic field. Analysis of monostatic reverberation data acquired during the Site A experiment (Run 1) of the Acoustic Reverberation Special Research Program 1993 Acoustics Cruise suggests that the scattered signals cannot be accounted for quantitatively in terms of large-scale slope, even though a strong correspondence between high intensity backscatter and seafloor ridges is observed. In order to investigate and quantify the actual sources of seafloor scattering, a numerical modeling study of seafloor models is undertaken using a finitedifference solution to the elastic wave equation. Geological data available at Site A and published reports describing geological properties of similar deep ocean crustal regions are used to develop a realistic seafloor model for the study area with realistic constraints on elastic parameters. Wavelength-scale heterogeneity in each model, in the form of seafloor roughness and subseafloor volume heterogeneity is defined using stochastic distributions with Gaussian autocorrelations. These distributions are quantified by their correlation lengths and standard deviation in amplitude. In order to incorporate all seafloor structure in a single parameterization of seafloor scattering, large-scale slope and wavelength-scale seafloor spatial parameters (rms height and correlation length), are included, along with the acoustic beam grazing-angle relative to a horizontal seafloor, in the definition of an 'effective grazing angle'. The Rayleigh roughness parameter, which depends on grazing angle of the insonification, is then redefined using the effective grazing angle and calculated for a variety of seafloor models. Scattering strengths are shown to vary systematically but nonlinearly with the 'effective Rayleigh roughness parameters' of horizontal rough seafloor models. This leads to an approximate interpretation scheme for backscatter intensity. In general, variation in backscattering is found to be dominated by the scattering from rough seafloor. If the seafloor is smooth or very low velocity (e.g., sediment), then scattering from volume heterogeneity becomes an important factor in the backscattered field. Both wavelength-scale seafloor roughness and volume heterogeneity are shown to be capable of producing the levels of variation in intensity observed in monostatic reverberation experiments. Variations in large-scale seafloor slope and subseafloor average velocity are shown to influence the backscatter response of seafloor models.by Robert John Greaves.Ph.D

Bathymetry and sediment thickness survey of the Hawaii-2 cable : cruise report for Kiwi expedition leg 2 on the R/V Roger Revelle

The primary purpose of this cruise was to identify at least two potential observatory sites along the Hawaii-2 cable that would be suitable for drilling a hole to basement. There is a funded program, the Hawaii-2 Observatory (H20), to install a junction box on the cable about mid-way between California and Hawaii (Figures 1 and 2). We want to identify sites in advance so that drilling will be possible near the observatory. This will permit a large range of borehole experiments to be cared out continuously and in real time. Based on available data we chose a section of cable between 140° and 143°W. This cable lies on a ribbon of 'normal' oceanic crust with well defined magnetic anomalies and relatively smooth bathymetry. The goals were to acquire SEABEAM bathymetry data and single channel seismic reflection data along this section of cable, to identify at least two potential sites along the cable and to car out SCS surveys within about 10km radius of the sites. Since the H20 cable has been given to the scientific community it is a valuable resource for research. While transiting to and from the site we felt that it would be wortwhile to acquire SEABEAM data along as much of the cable track as possible. This 'spec' data, Seabeam and magnetometer data between 130°W and 155°W may be useful to other investigators in the future.This work was carried out under the JOI Prime Contract OCE-93020477, JOI Budget Code 44505-J130l0

A novel method of strain - bending moment calibration for blade testing

A new method of interpreting strain data in full scale static and fatigue tests has been implemented as part of the Offshore Renewable Energy Catapult's ongoing development of biaxial fatigue testing of wind turbine blades. During bi-axial fatigue tests, it is necessary to be able to distinguish strains arising from the flapwise motion of the blade from strains arising from the edgewise motion. The method exploits the beam-like structure of blades and is derived using the equations of beam theory. It offers several advantages over the current state of the art method of calibrating strain gauges

A candidate fusion engineering material, WC-FeCr

A new candidate fusion engineering material, WC-FeCr, has been irradiated with He ions at 25 and 500 °C. Ions were injected at 6 keV to a dose of ~15 dpa and 50 at. % He, simulating direct helium injection from the plasma. The microstructural evolution was continuously characterised in situ using transmission electron microscopy. In the FeCr phase, a coarse array of 3–6 nm bubbles formed. In the WC, bubbles were less prominent and smaller (~2 nm). Spherical-cap bubbles formed at hetero-phase interfaces of tertiary precipitates, indicating that enhanced processing routes to minimise precipitation could further improve irradiation tolerance

Spiral Density Waves in a Young Protoplanetary Disk

Gravitational forces are expected to excite spiral density waves in protoplanetary disks, disks of gas and dust orbiting young stars. However, previous observations that showed spiral structure were not able to probe disk midplanes, where most of the mass is concentrated and where planet formation takes place. Using the Atacama Large Millimeter/submillimeter Array we detected a pair of trailing symmetric spiral arms in the protoplanetary disk surrounding the young star Elias 2-27. The arms extend to the disk outer regions and can be traced down to the midplane. These millimeter-wave observations also reveal an emission gap closer to the star than the spiral arms. We argue that the observed spirals trace shocks of spiral density waves in the midplane of this young disk.Comment: This is our own version of the manuscript, the definitive version was published in Science (DOI: 10.1126/science.aaf8296) on September 30, 2016. Posted to the arxiv for non-commercial us