9,203 research outputs found
Machine vision for space telerobotics and planetary rovers
Machine vision allows a non-contact means of determining the three-dimensional shape of objects in the environment, enabling the control of contact forces when manipulation by a telerobot or traversal by a vehicle is desired. Telerobotic manipulation in Earth orbit requires a system that can recognize known objects in spite of harsh lighting conditions and highly specular or absorptive surfaces. Planetary surface traversal requires a system that can recognize the surface shape and properties of an unknown and arbitrary terrain. Research on these two rather disparate types of vision systems is described
Time-delayed operation of a telerobot via geosynchronous relay
Operation of a telerobot is compromised if a time delay of more than a few hundred milliseconds exists between the operator and remote manipulator. However, the most economically attractive way to perform telerobotic functions such as assembly, maintenance, and repair in Earth orbit is via geosynchronous relay satellites to a ground-based operator. This induces loop delays from one-half to two seconds, depending on how many relays are involved. Such large delays makes direct master-slave, force-reflecting teleoperated systems infeasible. Research at JPL on a useful telerobot that operates with such time delays is described
Research-based assessment of students' beliefs about experimental physics: When is gender a factor?
The existence of gender differences in student performance on conceptual
assessments and their responses to attitudinal assessments has been repeatedly
demonstrated. This difference is often present in students' preinstruction
responses and persists in their postinstruction responses. However, one area in
which the presence of gender differences has not been extensively explored is
undergraduate laboratory courses. For example, one of the few laboratory
focused research-based assessments, the Colorado Learning Attitudes about
Science Survey for Experimental Physics (E-CLASS), has not been tested for the
existence of gender differences in students' responses. Here, we utilize a
national data set of responses to the E-CLASS to determine if they demonstrate
significant gender differences. We also investigate how these differences vary
along multiple student and course demographic slices, including course level
(first-year vs.\ beyond-first-year) and major (physics vs.\ non-physics). We
observe a gender gap in pre- and postinstruction E-CLASS scores in the
aggregate data both for the overall score and for most items individually.
However, for some subpopulations (e.g., beyond-first-year students) the size or
even existence of the gender gap depends on another dimension (e.g., student
major). We also find that for all groups the gap in postinstruction scores
vanishes or is greatly reduced when controlling for preinstruction scores,
course level, and student major.Comment: 11 pages, 3 figures, accepted to Phys. Rev. - PE
Students' views about the nature of experimental physics
The physics community explores and explains the physical world through a
blend of theoretical and experimental studies. The future of physics as a
discipline depends on training of students in both the theoretical and
experimental aspects of the field. However, while student learning within
lecture courses has been the subject of extensive research, lab courses remain
relatively under-studied. In particular, there is little, if any, data
available that addresses the effectiveness of physics lab courses at
encouraging students to recognize the nature and importance of experimental
physics within the discipline as a whole. To address this gap, we present the
first large-scale, national study ( and
) of undergraduate physics lab courses through analysis of
students' responses to a research-validated assessment designed to investigate
students' beliefs about the nature of experimental physics. We find that
students often enter and leave physics lab courses with ideas about
experimental physics as practiced in their courses that are inconsistent with
the views of practicing experimental physicists, and this trend holds at both
the introductory and upper-division levels. Despite this inconsistency, we find
that both introductory and upper-division students are able to accurately
predict the expert-like response even in cases where their views about
experimentation in their lab courses disagree. These finding have implications
for the recruitment, retention, and adequate preparation of students in
physics.Comment: 10 pages, 2 figures, Accepted to Phys. Rev. PE
Alternative potentials for the electromagnetic field
The electromagnetic field can be expressed in terms of two complex potentials
which are related to the Debye potentials. The evolution
equations for these potentials are derived, which are separable either in
parabolic coordinates (leading to the radiation fields) or in radial
coordinates (multipole fields). Potentials corresponding to focused wave fields
as well as plane waves are discussed. A conserved radiation density can be
constructed in terms of these potentials, which is positive (negative) for
positive (negative) helicity radiation.Comment: 13 pages, plainTex, slightly amended version of origina
Students' epistemologies about experimental physics: Validating the Colorado Learning Attitudes about Science Survey for Experimental Physics
Student learning in instructional physics labs represents a growing area of
research that includes investigations of students' beliefs and expectations
about the nature of experimental physics. To directly probe students'
epistemologies about experimental physics and support broader lab
transformation efforts at the University of Colorado Boulder (CU) and
elsewhere, we developed the Colorado Learning Attitudes about Science Survey
for Experimental Physics (E-CLASS). Previous work with this assessment has
included establishing the accuracy and clarity of the instrument through
student interviews and preliminary testing. Several years of data collection at
multiple institutions has resulted in a growing national data set of student
responses. Here, we report on results of the analysis of these data to
investigate the statistical validity and reliability of the E-CLASS as a
measure of students' epistemologies for a broad student population. We find
that the E-CLASS demonstrates an acceptable level of both validity and
reliability on measures of, item and test discrimination, test-retest
reliability, partial-sample reliability, internal consistency, concurrent
validity, and convergent validity. We also examine students' responses using
Principal Component Analysis and find that, as expected, the E-CLASS does not
exhibit strong factors.Comment: 10 pages, 4 figures, 7 tables, submitted to Phys. Rev. ST - PE
Improvement or selection? A longitudinal analysis of students' views about experimental physics in their lab courses
Laboratory courses represent a unique and potentially important component of
the undergraduate physics curriculum, which can be designed to allow students
to authentically engage with the process of experimental physics. Among other
possible benefits, participation in these courses throughout the undergraduate
physics curriculum presents an opportunity to develop students' understanding
of the nature and importance of experimental physics within the discipline as a
whole. Here, we present and compare both a longitudinal and pseudo-longitudinal
analysis of students' responses to a research-based assessment targeting
students' views about experimental physics -- the Colorado Learning Attitudes
about Science Survey for Experimental Physics (E-CLASS) -- across multiple,
required lab courses at a single institution. We find that, while
pseudo-longitudinal averages showed increases in students' E-CLASS scores in
each consecutive course, analysis of longitudinal data indicates that this
increase was not driven by a cumulative impact of laboratory instruction.
Rather, the increase was driven by a selection effect in which students who
persisted into higher-level lab courses already had more expert-like beliefs,
attitudes, and expectations than their peers when they started the lower-level
courses.Comment: 6 pages, 1 figure, submitted as a short paper to Phys. Rev. PE
High temperature deformation of dispersion strengthened nickel alloys. 1 - The influence of initial structure on tensile and creep deformation of TD nickel. 2 - The effect of matrix stacking fault energy on creep of Ni-Cr-ThO2 alloys Final report, 9 Feb. 1967 - 9 Feb. 1968
High temperature creep studies on unaltered, and recrystallized nickel alloy
The role of grain size and shape in the strengthening of dispersion hardened nickel alloys
Thermomechanical processing was used to develop various microsstructures in Ni, Ni-2ThO2, Ni-20Cr, Ni-20CR-2ThO2, Ni-20Cr-10W-and Ni-20Cr-10W-2ThO2. The yield strength at 25 C increased with substructure refinement according to the Hall-Petch relation, and substructure refinement was a much more potent means of strengthening than was dispersion hardening. At elevated temperature (1093 C), the most important microstructural feature affecting strength was the grain aspect ratio (grain length, L, divided by grain width, 1. The yield strength and creep strength increased linearly with increasing L/1
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