318 research outputs found
Running the Race: An Evaluation of Post-Race-to-the-Top Modifications to Teacher Tenure Laws and a Recommendation for Future Legislative Changes
Teacher tenure laws have been in existence for almost a century. However, in that time, teacher tenure has been under fire by individuals who consider it outdated and irrelevant. Additionally, teacher tenure laws have come under fire in recent decades due to a shift in education policy as a result of initiatives such as No Child Left Behind and Race to the Top. This article offers a closer look at the evolution of teacher tenure laws over the past century in order to understand and evaluate the wave of recent state legislation changes regarding teacher tenure laws. These changes, largely shaped by federal education policies, attempt to accomplish one of several goals: 1) allow districts to terminate a teacher’s employment based on the evaluations, 2) make it more difficult for teachers to attain tenure, and 3) eliminate seniority as a factor in determining which teachers should be terminated during times when the district must downsize its staff. This article evaluates how well current legislation addresses these concerns. This discussion culminates in a proposal to implement new legislation focused on extending teachers’ probationary periods before providing the benefits of tenure, incorporating more peer evaluations into measures of efficiency and effectiveness, and eliminating seniority as a consideration in reduction-in-force statutes
Surface mixed layer deepening through wind shear alignment in a seasonally stratified shallow sea
Turbulent mixing in a changing Arctic Ocean
© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Rippeth, T. P., & Fine, E. C. Turbulent mixing in a changing Arctic Ocean. Oceanography, 35(3-4), (2022), https://doi.org/10.5670/oceanog.2022.103.Historically, the Arctic Ocean has been considered an ocean of low variability and weak turbulent mixing. However, the decline in seasonal sea ice cover over the past couple of decades has led to increased coupling between the atmosphere and the ocean, with potential enhancement of turbulent mixing. Here, we review studies identifying energy sources and pathways that lead to turbulent mixing in an increasingly ice-free Arctic Ocean. We find that the evolution of wind-generated, near-inertial oscillations is highly sensitive to the seasonal sea ice cycle, but the response varies greatly between the continental shelves and the abyssal ocean and between the eastern and western ocean basins. There is growing interest in the role of tides and continental shelf waves in driving mixing over sloping topography. Both dissipate through the development of unsteady lee waves. The role eddies play in transporting shelf water into the basins and in supporting mixing has become more apparent as technological advances have permitted higher resolution observations of sea ice retreat. The importance of the dissipation of unsteady lee waves and of eddies in driving mixing highlights the need for parameterizations of these phenomena in regional ocean models and climate simulations.Tom Rippeth’s interest in the Arctic has been funded through 2 UKRI NERC Consortia (Asbo and Teacosi), and more recently through the UKRI NERC - German Federal Ministry for Science and Education (BMBF) Changing Arctic Programme PEANUTS project. Effie Fine’s interest in the Arctic has been supported by the US National Science Foundation’s Graduate Research Fellowships Program and Office of Polar Programs, by the Office of Naval Research, and by the Postdoctoral Scholar Program at Woods Hole Oceanographic Institution, with funding provided by the Weston Howland Jr. Postdoctoral Scholarship
Measuring Turbulent Dissipation Using a Tethered ADCP
The structure function method for estimating the dissipation rate of turbulent kinetic energy, previously validated for measurements from seabed fixed mounts, is applied to data from 1.2-MHz acoustic Doppler current profiler (ADCP) instruments operating in pulse�pulse coherent mode and mounted in midwater below a tethered buoy. Movements of the buoy introduce additional relative velocity components, but it is hypothesized that these flow components should not seriously interfere with the turbulence information because (i) horizontal or vertical translation induces the same flow component in all cells of an ADCP beam and (ii) any rotation of the instrument about its center induces flow components that are normal to the beam direction, and thus neither affect the structure function. This hypothesis is tested by comparing a series of dissipation measurements from a moored ADCP with those from a free-falling Vertical Microstructure Profiler (VMP) shear probe deployed from a nearby research vessel. The results indicate generally good conformity in both mean and variability over almost two decades of dissipation rates. The noise level of the structure function estimates with the pulse�pulse coherent ADCP is close to that of the VMP at ~3 � 10�10 W kg�1. This approach offers the prospect of long time series measurements of dissipation rate from moorings, albeit with restricted vertical range of a few meters
Impact of acoustic Doppler current profiler (ADCP) motion on structure function estimates of turbulent kinetic energy dissipation rate
Improving Word Sense Disambiguation in Neural Machine Translation with Salient Document Context
Lexical ambiguity is a challenging and pervasive problem in machine
translation (\mt). We introduce a simple and scalable approach to resolve
translation ambiguity by incorporating a small amount of extra-sentential
context in neural \mt. Our approach requires no sense annotation and no change
to standard model architectures. Since actual document context is not available
for the vast majority of \mt training data, we collect related sentences for
each input to construct pseudo-documents. Salient words from pseudo-documents
are then encoded as a prefix to each source sentence to condition the
generation of the translation. To evaluate, we release \docmucow, a challenge
set for translation disambiguation based on the English-German \mucow
\cite{raganato-etal-2020-evaluation} augmented with document IDs. Extensive
experiments show that our method translates ambiguous source words better than
strong sentence-level baselines and comparable document-level baselines while
reducing training costs
Observations of a diapycnal shortcut to adiabatic upwelling of Antarctic Circumpolar Deep Water
In the Southern Ocean, small-scale turbulence causes diapycnal mixing which influences important water mass transformations, in turn impacting large-scale ocean transports such as the Meridional Overturning Circulation (MOC), a key controller of Earth's climate. We present direct observations of mixing over the Antarctic continental slope between water masses that are part of the Southern Ocean MOC. A 12 h time series of microstructure turbulence measurements, hydrography, and velocity observations off Elephant Island, north of the Antarctic Peninsula, reveals two concurrent bursts of elevated dissipation of O(10�6)�W�kg�1, resulting in heat fluxes �10 times higher than basin-integrated Drake Passage estimates. This occurs across the boundary between adjacent adiabatic upwelling and downwelling overturning cells. Ray tracing to nearby topography shows mixing between 300 and 400 m is consistent with the breaking of locally generated internal tidal waves. Since similar conditions extend to much of the Antarctic continental slope where these water masses outcrop, diapycnal mixing may contribute significantly to upwelling
Correcting surface wave bias in structure function estimates of turbulent kinetic energy dissipation rate
The combination of acoustic Doppler current profilers and the structure function methodology provides an attractive approach to making extended time series measurements of oceanic turbulence (the rate of turbulent kinetic energy dissipation ε) from moorings. However, this study shows that for deployments in the upper part of the water column, estimates of ε will be biased by the vertical gradient in wave orbital velocities. To remove this bias, a modified structure function methodology is developed that exploits the differing length scale dependencies of the contributions to the structure function resulting from turbulent and wave orbital motions. The success of the modified method is demonstrated through a comparison of ε estimates based on data from instruments at three depths over a 3-month period under a wide range of conditions, with appropriate scalings for wind stress and convective forcing
A comparison of methods for estimating Reynolds stress from ADCP measurements in wavy environments
Author Posting. © American Meteorological Society, 2011. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 28 (2011): 1539–1553, doi:10.1175/JTECH-D-11-00001.1.Turbulent Reynolds stresses are now routinely estimated from acoustic Doppler current profiler (ADCP) measurements in estuaries and tidal channels using the variance method, yet biases due to surface gravity waves limit its use in the coastal ocean. Recent modifications to this method, including spatially filtering velocities to isolate the turbulence from wave velocities and fitting a cospectral model to the below-wave band cospectra, have been used to remove this bias. Individually, each modification performed well for the published test datasets, but a comparative analysis over the range of conditions in the coastal ocean has not yet been performed. This work uses ADCP velocity measurements from five previously published coastal ocean and estuarine datasets, which span a range of wave and current conditions as well as instrument configurations, to directly compare methods for estimating stresses in the presence of waves. The computed stresses from each were compared to bottom stress estimates from a quadratic drag law and, where available, estimates of wind stress. These comparisons, along with an analysis of the cospectra, indicated that spectral fitting performs well when the wave climate is wide-banded and/or multidirectional as well as when instrument noise is high. In contrast, spatial filtering performs better when waves are narrow-banded, low frequency, and when wave orbital velocities are strong relative to currents. However, as spatial filtering uses vertically separated velocity bins to remove the wave bias, spectral fitting is able to resolve stresses over a larger fraction of the water column.J. Rosman acknowledges funding
from the National Science Foundation (OCE-1061108)
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