10,647 research outputs found
The Market for Teacher Quality
Much of education policy focuses on improving teacher quality, but most policies lack strong research support. We use student achievement gains to estimate teacher value-added, our measure of teacher quality. The analysis reveals substantial variation in the quality of instruction, most of which occurs within rather than between schools. Although teacher quality appears to be unrelated to advanced degrees or certification, experience does matter -- but only in the first year of teaching. We also find that good teachers tend to be effective with all student ability levels but that there is a positive value of matching students and teachers by race. In the second part of the analysis, we show that teachers staying in our sample of urban schools tend to be as good as or better than those who exit. Thus, the main cost of large turnover is the introduction of more first year teachers. Finally, there is little or no evidence that districts that offer higher salaries and have better working conditions attract the higher quality teachers among those who depart the central city district. The overall results have a variety of direct policy implications for the design of school accountability and the compensation of teachers.
“Skittles & Red Bull is my favourite flavour”: E-cigarettes, smoking, vaping and the changing landscape of nicotine consumption amongst British teenagers – implications for the normalisation debate
Aims: From an academic discourse explaining trends in drug-related attitudes and behaviours, “normalisation” now also encompasses public health policy advocating “denormalisation” of smoking. This study explored young people’s attitudes and behaviours to cigarettes and e-cigarettes to ascertain whether a process of “renormalisation” was underway. Methods: A six-month multi-method study was conducted in NW England. Data collection in April-July 2014 included a convenience sample survey of 233 students; secondary analysis of a 3,500 respondent survey; stakeholder interviews; participant observation sessions; focus groups; and participatory research events with over 100 students. Findings: With the public performance of “vaping” valued as an indicator of experienced use, young people used e-cigarettes primarily for flavour combinations and to perform “tricks”. Smoking cessation and nicotine consumption were less important motivations. When comparing e-cigarettes with eight indicators of normalisation – additionally, legal status and risk perception – there were indications of a growing cultural accommodation of “vaping”. Conclusion: The changing landscape of nicotine and non-nicotine products challenges traditional conceptualisations of “smoking” and “non-smoking” and problematises the notion of linear processes of normalisation in respect not just of young people’s tobacco and nicotine use, but more generally, of delivery systems and the drugs dispensed within them, suggesting marketplace-differentiated normalisation
Quantum process tomography of a controlled-NOT gate
We demonstrate complete characterization of a two-qubit entangling process -
a linear optics controlled-NOT gate operating with coincident detection - by
quantum process tomography. We use maximum-likelihood estimation to convert the
experimental data into a physical process matrix. The process matrix allows
accurate prediction of the operation of the gate for arbitrary input states,
and calculation of gate performance measures such as the average gate fidelity,
average purity and entangling capability of our gate, which are 0.90, 0.83 and
0.73, respectively.Comment: 4 pages, 2 figures. v2 contains new data corresponding to improved
gate operation. Figure quality slightly reduced for arXi
Swift observations of the 2006 outburst of the recurrent nova RS Ophiuchi: II. 1D hydrodynamical models of wind driven shocks
Following the early Swift X-ray observations of the latest outburst of the
recurrent nova RS Ophiuchi in February 2006 (Paper I), we present new 1D
hydrodynamical models of the system which take into account all three phases of
the remnant evolution. The models suggest a novel way of modelling the system
by treating the outburst as a sudden increase then decrease in wind mass-loss
rate and velocity. The differences between this wind model and previous
Primakoff-type simulations are described. A more complex structure, even in 1D,
is revealed through the presence of both forward and reverse shocks, with a
separating contact discontinuity. The effects of radiative cooling are
investigated and key outburst parameters such as mass-loss rate, ejecta
velocity and mass are varied. The shock velocities as a function of time are
compared to the ones derived in Paper I. We show how the manner in which the
matter is ejected controls the evolution of the shock and that for a
well-cooled remnant, the shock deceleration rate depends on the amount of
energy that is radiated away.Comment: 9 pages, 5 figure
Labour efficiency on-farm
End of project reportImprovements in milking efficiency have a greater influence than any other aspect of the dairy farmers work on overall farm labour inputs (Whipp, 1992). In order to facilitate the examination of milking process labour inputs, the milking process may be divided into the following three components: herding pre and post milking (transfer of cows to and from the milking parlour); milking (milking tasks / work routines within the parlour); and washing (washing of milking machine and yard). Meanwhile, within milking specifically, the number of cows milked per operator per hour is the best measure of both the performance of the operator and the milking installation (Clough, 1978). This is affected by the following three factors: the milking times of the cows, the number and arrangement of the milking units, and the operator’s work routine (Whipp, 1992). The addition of extra milking units will only increase milking performance if the operator has idle time during milking (Hansen, 1999)
The H.E.S.S. II GRB Program
Gamma-ray bursts (GRBs) are some of the most energetic and exotic events in
the Universe, however their behaviour at the highest energies (>10 GeV) is
largely unknown. Although the Fermi-LAT space telescope has detected several
GRBs in this energy range, it is limited by the relatively small collection
area of the instrument. The H.E.S.S. experiment has now entered its second
phase by adding a fifth telescope of 600 m mirror area to the centre of
the array. This new telescope increases the energy range of the array, allowing
it to probe the sub-100 GeV range while maintaining the large collection area
of ground based gamma-ray observatories, essential to probing short-term
variability at these energies. We will present a description of the GRB
observation scheme used by the H.E.S.S. experiment, summarising the behaviour
and performance of the rapid GRB repointing system, the conditions under which
potential GRB repointings are made and the data analysis scheme used for these
observations.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherland
Van Allen Probes show that the inner radiation zone contains no MeV electrons: ECT/MagEIS data
Abstract
We present Van Allen Probe observations of electrons in the inner radiation zone. The measurements were made by the Energetic Particle, Composition, and Thermal Plasma/Magnetic Electron Ion Spectrometer (MagEIS) sensors that were designed to measure electrons with the ability to remove unwanted signals from penetrating protons, providing clean measurements. No electrons \u3e900 keV were observed with equatorial fluxes above background (i.e., \u3e0.1 el/(cm2 s sr keV)) in the inner zone. The observed fluxes are compared to the AE9 model and CRRES observations. Electron fluxes \u3c200 keV exceeded the AE9 model 50% fluxes and were lower than the higher-energy model fluxes. Phase space density radial profiles for 1.3 ≤ L* \u3c 2.5 had mostly positive gradients except near L*~2.1, where the profiles for μ = 20–30 MeV/G were flat or slightly peaked. The major result is that MagEIS data do not show the presence of significant fluxes of MeV electrons in the inner zone while current radiation belt models and previous publications do
GMRT Observations of the 2006 outburst of the Nova RS Ophiuchi: First detection of emission at radio frequencies < 1.4 GHz
The first low radio frequency (<1.4 GHz) detection of the outburst of the
recurrent nova RS Ophiuchi is presented in this letter. Radio emission was
detected at 0.61 GHz on day 20 with a flux density of ~48 mJy and at 0.325 GHz
on day 38 with a flux density of ~ 44 mJy. This is in contrast with the 1985
outburst when it was not detected at 0.327 GHz even on day 66. The emission at
low radio frequencies is clearly non-thermal and is well-explained by a
synchrotron spectrum of index alpha ~ -0.8 (S propto nu^alpha) suffering
foreground absorption due to the pre-existing, ionized, warm, clumpy red giant
wind. The absence of low frequency radio emission in 1985 and the earlier
turn-on of the radio flux in the current outburst are interpreted as being due
to higher foreground absorption in 1985 compared to that in 2006, suggesting
that the overlying wind densities in 2006 are only ~30% of those in 1985.Comment: 14 pages, 1 figure. Accepted for publication in ApJ
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