25,484 research outputs found
Toolboxes and handing students a hammer: The effects of cueing and instruction on getting students to think critically
Developing critical thinking skills is a common goal of an undergraduate
physics curriculum. How do students make sense of evidence and what do they do
with it? In this study, we evaluated students' critical thinking behaviors
through their written notebooks in an introductory physics laboratory course.
We compared student behaviors in the Structured Quantitative Inquiry Labs
(SQILabs) curriculum to a control group and evaluated the fragility of these
behaviors through procedural cueing. We found that the SQILabs were generally
effective at improving the quality of students' reasoning about data and making
decisions from data. These improvements in reasoning and sensemaking were
thwarted, however, by a procedural cue. We describe these changes in behavior
through the lens of epistemological frames and task orientation, invoked by the
instructional moves
Cosmic Rays from Gamma Ray Bursts in the Galaxy
The rate of terrestrial irradiation events by galactic gamma-ray bursts
(GRBs) is estimated using recent standard-energy results. We assume that GRBs
accelerate high-energy cosmic rays, and present results of three-dimensional
simulations of cosmic rays moving in the Galactic magnetic field and diffusing
through pitch-angle scattering. An on-axis GRB extinction event begins with a
powerful prompt gamma-ray and neutron pulse, followed by a longer-lived phase
from cosmic-ray protons and neutron-decay protons that diffuse towards Earth.
Our results force a reinterpretation of reported ~ 10^{18} eV cosmic-ray
anisotropies and offer a rigorous test of the model where high-energy cosmic
rays originate from GRBs, which will soon be tested with the Auger Observatory.Comment: 9 pages, 4 figures, ApJ Letters, in press. Clarified limit of
test-particle approximation, prediction that Auger will not confirm SUGAR
source. (Data may not appear onscreen at low magnification.) Simulations at
http://heseweb.nrl.navy.mil/gamma/~dermer/invest/sim/index.ht
Overview of the Tevatron Collider Complex: Goals, Operations and Performance
For more than two decades the Tevatron proton-antiproton collider was the
centerpiece of the world's high energy physics program. The collider was
arguably one of the most complex research instruments ever to reach the
operation stage and is widely recognized for numerous physics discoveries and
for many technological breakthroughs. In this article we outline the historical
background that led to the construction of the Tevatron Collider, the strategy
applied to evolution of performance goals over the Tevatron's operational
history, and briefly describe operations of each accelerator in the chain and
achieved performance.Comment: Includes modifications suggested by reviewer
Advances in large-diameter liquid encapsulated Czochralski GaAs
The purity, crystalline perfection, and electrical properties of n- and p-type GaAs crystals grown by the liquid encapsulated Czochralski (LEC) technique are evaluated. The determination of the dislocation density, incidence of twinning, microstructure, background purity, mobility, and minority carrier diffusion length is included. The properties of the LEC GaAs crystals are generally comparable to, if not superior to those of small-diameter GaAs material grown by conventional bulk growth techniques. As a result, LEC GaAs is suitable for application to minority carrier devices requiring high-quality and large-area substrates
High purity low dislocation GaAs single crystals
Recent advances in GaAs bulk crystal growth using the LEC (liquid encapsulated Czochralski) technique are described. The dependence of the background impurity concentration and the dislocation density distribution on the materials synthesis and growth conditions were investigated. Background impurity concentrations as low as 4 x 10 to the 15th power were observed in undoped LEC GaAs. The dislocation density in selected regions of individual ingots was very low, below the 3000 cm .3000/sq cm threshold. The average dislocation density over a large annular ring on the wafers fell below the 10000/sq cm level for 3 inch diameter ingots. The diameter control during the program advanced to a diameter variation along a 3 inch ingot less than 2 mm
Application of inertial instruments for DSN antenna pointing and tracking
The feasibility of using inertial instruments to determine the pointing attitude of the NASA Deep Space Network antennas is examined. The objective is to obtain 1 mdeg pointing knowledge in both blind pointing and tracking modes to facilitate operation of the Deep Space Network 70 m antennas at 32 GHz. A measurement system employing accelerometers, an inclinometer, and optical gyroscopes is proposed. The initial pointing attitude is established by determining the direction of the local gravity vector using the accelerometers and the inclinometer, and the Earth's spin axis using the gyroscopes. Pointing during long-term tracking is maintained by integrating the gyroscope rates and augmenting these measurements with knowledge of the local gravity vector. A minimum-variance estimator is used to combine measurements to obtain the antenna pointing attitude. A key feature of the algorithm is its ability to recalibrate accelerometer parameters during operation. A survey of available inertial instrument technologies is also given
'I was really upset and it put me off': The emotional impact of assessment feedback on first-year undergraduate students
Assessment feedback can have an emotional impact on students. This qualitative research contributes to the existing body of literature on students' emotional reactions to assessment feedback by investigating the negative responses to summative feedback experienced by first-year students at two UK universities. The majority of the learners interviewed indicated that their initial first-year feedback had a negative emotional impact and demotivated them. For some students, these negative emotions were very serious and led them to consider leaving university. Negative emotions were related to the written feedback provided, the grade received, and the student's expectations about both. Potential solutions to mitigate first-year students' negative emotional reactions to summative assessment feedback are provided
- …