1,007 research outputs found
Application of a discrete element model to the analysis of granular soil recovery in an offshore tubular vibrocore
As the human need for ocean resources accelerates, offshore geotechnics continues to grow and become ever more relevant. Seabed soil sampling is crucial in deep-water engineering projects or geological studies where a detailed knowledge of the seabed geology is required. Deep-sea vibrocoring is a relatively new offshore sampling technique. The system consists of a vertical, tubular core barrel with a sharp cutting edge at its lower end vibrated into the seabed by a high-frequency, low-amplitude vibratory motor. In the past, success of a coring operation has been judged primarily by the length of the recovered core. More recently, studies have given focus to the problems associated with achieving soil specimens in which the in-situ sedimentary structure is preserved. In practice, the core recovery ratio - defined as the ratio between the sampled length of core sediment and the length of core barrel penetrated into the soil - is frequently less than unity. Literature suggests that the physical processes governing the dynamic interaction between core barrel and soil are poorly understood. Through review of relevant literature, and the execution of both physical testing and numerical modelling, this study aimed to a) Develop a calibrated 30 discrete element model of a given vibrocore-soil system, and b) Investigate the soil mechanics phenomena influencing the disturbance and recovery of vibrocore soil samples
Ball pen probe in strongly magnetised RF plasmas
A study of ball pen probes (BPPs) in a rf strongly magnetised plasma is reported for the first time. These probes have been successfully used in fusion plasmas, with magnetic fields up to 2.5 T, to measure the plasma potential. In this paper experimental results of various ball pen designs (2 and 4 mm diameter with flat and conical collectors) are presented up to 0.5 T in a low pressure capacitively coupled rf plasma. A theory of the BPP is developed, showing that the increase of the collector potential and plateau region, with collector retraction, requires the electron current to decrease faster than the ion current. Experimentally, it is found that to develop effective electron screening the electron Larmor radius should be smaller than the tunnel internal diameter. Smaller tunnels improve screening due to the tunnel entrance wall sheaths. Inside the tunnel a plateau region forms at 81 mT reducing to a broad peak at higher field strengths. Ion shielding and surface losses (for small tunnel diameters) reduce the collector peak width and maximum potential with increasing magnetic field. Conical collectors were found to increase the length of the plateau region and broaden the peak. Particle in cell simulations were in good agreement with the experimental results. The electron shielding and plateau regions were reproduced but not the broad peak at higher field strengths. Good agreement between both 2 mm BPPs and an emissive probe was found only at 81 mT to within 3 V or 1.3 electron temperatures (T e). For all BPPs at higher field strengths (≥ 250 mT) the maximum collector potential underestimated the emissive probe by more than 2.7 T e (7 V). At these field strengths all BPPs agree with each other to within 1.5 T e (4.1 V). Possible reasons for these disagreements are discussed
Altering visual feedback conditions impacts on postural sway performance in children after controlling for body mass index and habitual physical activity
Star formation concentration as a tracer of environmental quenching in action: a study of the Eagle and C-Eagle simulations
We study environmental quenching in the Eagle}/C-Eagle cosmological
hydrodynamic simulations over the last 11 Gyr (i.e. ). The simulations
are compared with observations from the SAMI Galaxy Survey at . We focus
on satellite galaxies in galaxy groups and clusters (
< ). A star-formation
concentration index [-index ] is defined, which measures how concentrated star
formation is relative to the stellar distribution. Both Eagle/C-Eagle and SAMI
show a higher fraction of galaxies with low -index in denser environments at
. Low -index galaxies are found below the SFR- main
sequence (MS), and display a declining specific star formation rate (sSFR) with
increasing radii, consistent with ``outside-in'' environmental quenching.
Additionally, we show that -index can be used as a proxy for how long
galaxies have been satellites. These trends become weaker at increasing
redshift and are absent by . We define a quenching timescale as how long it takes satellites to transition from the MS to the
quenched population. We find that simulated galaxies experiencing
``outside-in'' environmental quenching at low redshift () have a
long quenching timescale (median > 2 Gyr). The simulated
galaxies at higher redshift () experience faster quenching (median
< 2Gyr). At galaxies undergoing environmental
quenching have decreased sSFR across the entire galaxy with no ``outside-in''
quenching signatures and a narrow range of -index, showing that on average
environmental quenching acts differently than at .Comment: 21 pages, 17 figures
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A content analysis of research on technology use for teaching mathematics to students with disabilities: word networks and topic modeling
Authors of article conduct a content analysis of research on technology use for teaching mathematics to students with disabilities. They applied word networks and structural topic modeling of 488 studies published from 1980 to 2021. Results showed that the words “computer” and “computer-assisted instruction” had the highest degree of centrality in the 1980s and 1990s, and “learning disability” was another central word in the 2000s and 2010s
Design and sensitivity of a 6-axis seismometer for gravitational wave observatories
We present the design, control system, and noise analysis of a 6-axis seismometer comprising a mass suspended by a single fused silica fiber. We utilize custom-made, compact Michelson interferometers for the readout of the mass motion relative to the table and successfully overcome the sensitivity of existing commercial seismometers by over an order of magnitude in the angular degrees of freedom. We develop the sensor for gravitational-wave observatories, such as LIGO, Virgo, and KAGRA, to help them observe intermediate-mass black holes, increase their duty cycle, and improve localization of sources. Our control system and its achieved sensitivity makes the sensor suitable for other fundamental physics experiments, such as tests of semiclassical gravity, searches for bosonic dark matter, and studies of the Casimir force
Design and sensitivity of a 6-axis seismometer for gravitational wave observatories
We present the design, control system, and noise analysis of a 6-axis seismometer comprising a mass suspended by a single fused silica fiber. We utilize custom-made, compact Michelson interferometers for the readout of the mass motion relative to the table and successfully overcome the sensitivity of existing commercial seismometers by over an order of magnitude in the angular degrees of freedom. We develop the sensor for gravitational-wave observatories, such as LIGO, Virgo, and KAGRA, to help them observe intermediate-mass black holes, increase their duty cycle, and improve localization of sources. Our control system and its achieved sensitivity makes the sensor suitable for other fundamental physics experiments, such as tests of semiclassical gravity, searches for bosonic dark matter, and studies of the Casimir force
Design and sensitivity of a 6-axis seismometer for gravitational wave observatories
We present the design, control system, and noise analysis of a 6-axis
seismometer comprising a mass suspended by a single fused silica fibre. We
utilise custom-made, compact Michelson interferometers for the readout of the
mass motion relative to the table and successfully overcome the sensitivity of
existing commercial seismometers by over an order of magnitude in the angular
degrees of freedom. We develop the sensor for gravitational-wave observatories,
such as LIGO, Virgo, and KAGRA, to help them observe intermediate-mass black
holes, increase their duty cycle, and improve localisation of sources. Our
control system and its achieved sensitivity makes the sensor suitable for other
fundamental physics experiments, such as tests of semiclassical gravity,
searches for bosonic dark matter, and studies of the Casimir force
The SAMI Galaxy Survey: Environmental analysis of the orbital structures of passive galaxies
Most dynamical models of galaxies to date assume axisymmetry, which is not
representative of a significant fraction of massive galaxies. We have built
triaxial orbit-superposition Schwarzschild models of galaxies observed by the
SAMI Galaxy Survey, in order to reconstruct their inner orbital structure and
mass distribution. The sample consists of 153 passive galaxies with total
stellar masses in the range to . We present an
analysis of the internal structures and intrinsic properties of these galaxies
as a function of their environment. We measure their environment using three
proxies: central or satellite designation, halo mass and local nearest
neighbour galaxy density. We find that although these intrinsic properties
correlate most strongly with stellar mass, environment does play a secondary
role: at fixed stellar mass, galaxies in the densest regions are more radially
anisotropic. In addition, central galaxies, and galaxies in high local
densities show lower values of edge-on spin parameter proxy \lam. We also find
suggestions of a possible trend of the fractions of orbits with environment for
lower-mass galaxies (between and ) such that, at
fixed stellar mass, galaxies in higher local densities and halo mass have
higher fractions of hot orbits and lower fractions of warm orbits. Our results
demonstrate that after stellar mass, environment does play a role in shaping
present-day passive galaxies.Comment: 21 pages. Accepted for publication in MNRA
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