73,971 research outputs found
Observations of the Vertical Structure of Tidal Currents in Two Inlets
Observations of the vertical structure of broad band tidal currents were obtained at two energetic inlets. Each experiment took place over a 4 week period, the first at Hampton Inlet in southeastern New Hampshire, USA, in the Fall of 2011, and the second at New River Inlet in southern North Carolina, USA, in the spring of 2012. The temporal variation and vertical structure of the currents were observed at each site with 600 kHz and 1200 kHz RDI Acoustic Doppler Current Profilers (ADCP) deployed on low-profile bottom tripods in 7.5 and 12.5 m water depths near the entrance to Hampton Inlet, and in 8 and 9 m water depth within and outside New River Inlet, respectively. In addition, a Nortek Aquapro ADCP was mounted on a jetted pipe in about 2.5 m water depth on the flank of the each inlet channel. Flows within the Hampton/Seabrook Inlet were dominated by semi-diurnal tides ranging 2.5 - 4 m in elevation, with velocities exceeding 2.5 m/s. Flows within New River inlet were also semi-diurnal with tides ranging about 1 – 1.5 m in elevation and with velocities exceeding 1.5 m/s. Vertical variation in the flow structure at the dominant tidal frequency are examined as a function of location within and near the inlet. Outside the inlet, velocities vary strongly over the vertical, with a nearly linear decay from the surface to near the bottom. The coherence between the upper most velocity bin and the successively vertically separated bins drops off quickly with depth, with as much as 50% coherence decay over the water column. The phase relative to the uppermost velocity bin shifts over depth, with as much as 40 deg phase lag over the vertical, with bottom velocities leading the surface. Offshore, rotary coefficients indicate a stable ellipse orientation with rotational directions consistent over the vertical. At Hampton, the shallower ADCP, but still outside the inlet, shows a rotational structure that changes sign in the vertical indicating a sense of rotation at the bottom that is opposite to that at the surface. Within the inlet, the flow is more aligned with the channel, the decay in amplitude over the vertical is diminished, the coherence and phase structure is nearly uniform, and the rotary coefficients indicate no sense of rotation in the flow. The observations are qualitatively consistent with behavior described by Prandle (1982) for shallow water tidal flows
Self-Organizing Time Map: An Abstraction of Temporal Multivariate Patterns
This paper adopts and adapts Kohonen's standard Self-Organizing Map (SOM) for
exploratory temporal structure analysis. The Self-Organizing Time Map (SOTM)
implements SOM-type learning to one-dimensional arrays for individual time
units, preserves the orientation with short-term memory and arranges the arrays
in an ascending order of time. The two-dimensional representation of the SOTM
attempts thus twofold topology preservation, where the horizontal direction
preserves time topology and the vertical direction data topology. This enables
discovering the occurrence and exploring the properties of temporal structural
changes in data. For representing qualities and properties of SOTMs, we adapt
measures and visualizations from the standard SOM paradigm, as well as
introduce a measure of temporal structural changes. The functioning of the
SOTM, and its visualizations and quality and property measures, are illustrated
on artificial toy data. The usefulness of the SOTM in a real-world setting is
shown on poverty, welfare and development indicators
ILR Research in Progress 2013-14
The production of scholarly research continues to be one of the primary missions of the ILR School. During a typical academic year, ILR faculty members published or had accepted for publication over 25 books, edited volumes, and monographs, 170 articles and chapters in edited volumes, numerous book reviews. In addition, a large number of manuscripts were submitted for publication, presented at professional association meetings, or circulated in working paper form. Our faculty's research continues to find its way into the very best industrial relations, social science and statistics journals.Research_in_Progress_2013_14.pdf: 54 downloads, before Oct. 1, 2020
Age-related changes in matching novel objects across viewpoints
Peer reviewedPreprin
An ancestral axial twist explains the contralateral forebrain and the optic chiasm in vertebrates
Among the best-known facts of the brain are the contralateral visual,
auditory, sensational, and motor mappings in the forebrain. How and why did
these evolve? The few theories to this question provide functional answers,
such as better networks for visuomotor control. However, these theories
contradict the data, as discussed here. Instead we propose that a 90-deg
left-turn around the body-axis evolved in a common ancestor of all vertebrates.
Compensatory migrations of the tissues during development restore body
symmetry. Eyes, nostrils and forebrain compensate in the direction of the turn,
whereas more caudal structures migrate in the opposite direction. As a result
of these opposite migrations the forebrain becomes crossed and inverted with
respect to the rest of the nervous system. We show that these compensatory
migratory movements can indeed be observed in the zebrafish (Danio rerio) and
the chick (Gallus gallus). With a model we show how the axial twist hypothesis
predicts that an optic chiasm should develop on the ventral side of the brain,
whereas the olfactory tract should be uncrossed. In addition, the hypothesis
explains the decussation of the trochlear nerve, why olfaction is non-crossed,
why the cerebellar hemispheres represent the ipsilateral bodyside, why in
sharks the forebrain halves each represent the ipsilateral eye, why the heart
and other inner organs are asymmetric in the body. Due to the poor fossil
record, the possible evolutionary scenarios remain speculative. Molecular
evidence does support the hypothesis. The findings may throw new insight on the
problematic structure of the forebrain.Comment: 13 pages, 6 figures. A small correction is made (May 2014): see
footnote
Special Relativistic Magnetohydrodynamic Simulation of Two-Component Outflow Powered by Magnetic Explosion on Compact Stars
The nonlinear dynamics of outflows driven by magnetic explosion on the
surface of a compact star is investigated through special relativistic
magnetohydrodynamic simulations. We adopt, as the initial equilibrium state, a
spherical stellar object embedded in hydrostatic plasma which has a density
and is threaded by a dipole magnetic field. The
injection of magnetic energy at the surface of compact star breaks the
equilibrium and triggers a two-component outflow. At the early evolutionary
stage, the magnetic pressure increases rapidly around the stellar surface,
initiating a magnetically driven outflow. A strong forward shock driven outflow
is then excited. The expansion velocity of the magnetically driven outflow is
characterized by the Alfv\'en velocity on the stellar surface, and follows a
simple scaling relation . When the
initial density profile declines steeply with radius, the strong shock is
accelerated self-similarly to relativistic velocity ahead of the magnetically
driven component. We find that it evolves according to a self-similar relation
, where is the Lorentz
factor of the plasma measured at the shock surface . Purely
hydrodynamic process would be responsible for the acceleration mechanism of the
shock driven outflow. Our two-component outflow model, which is the natural
outcome of the magnetic explosion, can provide a better understanding of the
magnetic active phenomena on various magnetized compact stars.Comment: Accepted for publication in ApJ. 15 pages, 2 tables, 17 figure
For Our Information, Volume 14 (September 1961-June 1962)
An official publication of the ILR School, Cornell University, “for the information of all faculty, staff and students.
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