29,291 research outputs found
Revelation and the End of All Things
Author: Koester, Craig R. Title: Revelation and the end of all things. Publisher: Grand Rapids: Eerdmans, 2001
Deterrence of Corporate Fraud Through Securities Litigation: The Role of Institutional Investors
Johnson suggests that institutions are uniquely positioned to enhance the deterrence function of securities litigation without undermining the compensation goal
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Near-Infrared Broad-Line Profiles In Low-Redshift QSOs
We present near-infrared and optical spectrophotometry of six low-redshift QSOs. The integrated Pa-alpha/H-alpha-ratios cluster near the value 0.1, with one exception having a larger ratio consistent with other evidence of reddening. At least two of the Pa-alpha/H-alpha-profile ratios decrease with observed velocity. We discuss some implications for the dynamics of the broad-line region and this ratio's usefulness as a reddening indicator. We also present a spectrum of the He I-lambda-10830, Pa-lambda-blend of 1226 + 023. The He I/H-alpha-profile ratio shows marginal evidence for decreasing with observed velocity, which is consistent with the interpretation for the Pa-alpha/H-alpha-profile ratios.NSF 84-14652McDonald Observator
Kinematic analysis of the ARID manipulator
The kinematic structure of the ARID manipulator lends itself to simple forward and inverse kinematics analysis. The purpose of this paper is to fully document and verify an existing analysis. The symbolic software package MATHEMATICA was used to produce and verify the equations presented here. In the analysis to follow, the standard Devenit-Hartenberg kinematic parameters of the ARID were employed
Possible biomedical applications and limitations of a variable-force centrifuge on the lunar surface: A research tool and an enabling resource
Centrifuges will continue to serve as a valuable research tool in gaining an understanding of the biological significance of the inertial acceleration due to gravity. Space- and possibly lunar-based centrifuges will play a significant and enabling role with regard to the human component of future lunar and martian exploration, both as a means of accessing potential health and performance risks and as a means of alleviating these risks. Lunar-based centrifuges could be particularly useful as part of a program of physiologic countermeasures designed to alleviate the physical deconditioning that may result from prolonged exposure to a 1/6-g environment. Centrifuges on the lunar surface could also be used as part of a high-fidelity simulation of a trip to Mars. Other uses could include crew readaptation to 1 g, waste separation, materials processing, optical mirror production in situ on the Moon, and laboratory specimen separation
Calibration of the ARID robot
The author has formulated a new, general model for specifying the kinematic properties of serial manipulators. The new model kinematic parameters do not suffer discontinuities when nominally parallel adjacent axes deviate from exact parallelism. From this new theory the author develops a first-order, lumped-parameter, calibration-model for the ARID manipulator. Next, the author develops a calibration methodology for the ARID based on visual and acoustic sensing. A sensor platform, consisting of a camera and four sonars attached to the ARID end frame, performs calibration measurements. A calibration measurement consists of processing one visual frame of an accurately placed calibration image and recording four acoustic range measurements. A minimum of two measurement protocols determine the kinematics calibration-model of the ARID for a particular region: assuming the joint displacements are accurately measured, the calibration surface is planar, and the kinematic parameters do not vary rapidly in the region. No theoretical or practical limitations appear to contra-indicate the feasibility of the calibration method developed here
Accretion in giant planet circumplanetary disks
During the final growth phase of giant planets, accretion is thought to be
controlled by a surrounding circumplanetary disk. Current astrophysical
accretion disk models rely on hydromagnetic turbulence or gravitoturbulence as
the source of effective viscosity within the disk. However, the
magnetically-coupled accreting region in these models is so limited that the
disk may not support inflow at all radii, or at the required rate. Here, we
examine the conditions needed for self-consistent accretion, in which the disk
is susceptible to accretion driven by magnetic fields or gravitational
instability. We model the disk as a Shakura-Sunyaev disk and calculate
the level of ionisation, the strength of coupling between the field and disk
using Ohmic, Hall and Ambipolar diffusevities for both an MRI and vertical
field, and the strength of gravitational instability. We find that the standard
constant- disk is only coupled to the field by thermal ionisation
within with strong magnetic diffusivity prohibiting accretion through
the bulk of the midplane. In light of the failure of the constant- disk
to produce accretion consistent with its viscosity we drop the assumption of
constant- and present an alternate model in which varies
radially according to the level magnetic turbulence or gravitoturbulence. We
find that a vertical field may drive accretion across the entire disk, whereas
MRI can drive accretion out to , beyond which Toomre's and
gravitoturbulence dominates. The disks are relatively hot (K),
and consequently massive ().Comment: 19 pages, 5 figures, 2 tables; accepted for publication by MNRA
Magnetic fields in gaps surrounding giant protoplanets
Giant protoplanets evacuate a gap in their host protoplanetary disc, which
gas must cross before it can be accreted. A magnetic field is likely carried
into the gap, potentially influencing the flow. Gap crossing has been simulated
with varying degrees of attention to field evolution (pure hydrodynamical,
ideal, and resistive MHD), but as yet there has been no detailed assessment of
the role of the field accounting for all three key non-ideal MHD effects: Ohmic
resistivity, ambipolar diffusion, and Hall drift. We present a detailed
investigation of gap magnetic field structure as determined by non-ideal
effects. We assess susceptibility to turbulence induced by the
magnetorotational instability, and angular momentum loss from large-scale
fields. As full non-ideal simulations are computationally expensive, we take an
a posteriori approach, estimating MHD quantities from the pure hydrodynamical
gap crossing simulation by Tanigawa et al. (2012). We calculate the ionisation
fraction and estimate field strength and geometry to determine the strength of
non-ideal effects. We find that the protoplanetary disc field would be easily
drawn into the gap and circumplanetary disc. Hall drift dominates, so that much
of the gap is conditionally MRI unstable depending on the alignment of the
field and disc rotation axes. Field alignment also influences the strong
toroidal field component permeating the gap. Large-scale magnetic forces are
small in the circumplanetary disc, indicating they cannot drive accretion
there. However, turbulence will be key during satellite growth as it affects
critical disc features, such as the location of the ice line.Comment: 14 pages, 6 figures, accepted for publication by MNRA
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