4,370 research outputs found
Constraining the origin of the planetary debris surrounding ZTF J0139+5245 through rotational fission of a triaxial asteroid
White dwarfs containing orbiting planetesimals or their debris represent crucial benchmarks by which theoretical investigations of post-main-sequence planetary systems may be calibrated. The photometric transit signatures of likely planetary debris in the ZTF J0139+5245 white dwarf system have an orbital period of about 110 d. An asteroid which breaks up to produce this debris may spin itself to destruction through repeated close encounters with the star without entering its Roche radius and without influence from the white dwarf’s luminosity. Here, we place coupled constraints on the orbital pericentre (q) and the ratio (β) of the middle to longest semiaxes of a triaxial asteroid which disrupts outside of this white dwarf’s Roche radius (rRoche) soon after attaining its 110-d orbit. We find that disruption within tens of years is likely when β ≲ 0.6 and q ≈ 1.0–2.0rRoche, and when β ≲ 0.2 out to q ≈ 2.5rRoche. Analysing the longer time-scale disruption of triaxial asteroids around ZTF J0139+5245 is desirable but may require either an analytical approach relying on ergodic theory or novel numerical techniques
Instructor perspectives on iteration during upper-division optics lab activities
Although developing proficiency with modeling is a nationally endorsed
learning outcome for upper-division undergraduate physics lab courses, no
corresponding research-based assessments exist. Our longterm goal is to develop
assessments of students' modeling ability that are relevant across multiple
upper-division lab contexts. To this end, we interviewed 19 instructors from 16
institutions about optics lab activities that incorporate photodiodes.
Interviews focused on how those activities were designed to engage students in
some aspects of modeling. We find that, according to many interviewees,
iteration is an important aspect of modeling. In addition, interviewees
described four distinct types of iteration: revising apparatuses, revising
models, revising data-taking procedures, and repeating data collection using
existing apparatuses and procedures. We provide examples of each type of
iteration, and discuss implications for the development of future modeling
assessments.Comment: 4 pages, 1 figure; under revie
Access to undergraduate research experiences at a large research university
The American Physical Society recently released a statement calling on all
university physics departments to provide or facilitate access to research
experiences for all undergraduate students. In response, we investigated the
current status of access to undergraduate research at University of Colorado
Boulder (CU), a large research institution where the number of undergraduate
physics majors outnumber faculty by roughly ten to one. We created and
administered two surveys within CU's Physics Department: one probed
undergraduate students' familiarity with, and participation in, research; the
other probed faculty members' experiences as research mentors to
undergraduates. We describe the development of these instruments, our results,
and our corresponding evidence-based recommendations for improving local access
to undergraduate research experiences. Reflecting on our work, we make several
connections to an institutional change framework and note how other
universities and colleges might adapt our process.Comment: 4 pages, 3 figures, 1 table; Submitted to 2015 PERC Proceeding
Student ownership of projects in an upper-division optics laboratory course: A multiple case study of successful experiences
We investigate students' sense of ownership of multiweek final projects in an
upper-division optics lab course. Using a multiple case study approach, we
describe three student projects in detail. Within-case analyses focused on
identifying key issues in each project, and constructing chronological
descriptions of those events. Cross-case analysis focused on identifying
emergent themes with respect to five dimensions of project ownership: student
agency, instructor mentorship, peer collaboration, interest and value, and
affective responses. Our within- and cross-case analyses yielded three major
findings. First, coupling division of labor with collective brainstorming can
help balance student agency, instructor mentorship, and peer collaboration.
Second, students' interest in the project and perceptions of its value can
increase over time; initial student interest in the project topic is not a
necessary condition for student ownership of the project. Third, student
ownership is characterized by a wide range of emotions that fluctuate as
students alternate between extended periods of struggle and moments of success
while working on their projects. These findings not only extend the literature
on student ownership into a new educational domain---namely, upper-division
physics labs---they also have concrete implications for the design of
experimental physics projects in courses for which student ownership is a
desired learning outcome. We describe the course and projects in sufficient
detail that others can adapt our results to their particular contexts.Comment: 22 pages, 3 tables, submitted to Phys. Rev. PE
Using think-aloud interviews to characterize model-based reasoning in electronics for a laboratory course assessment
Models of physical systems are used to explain and predict experimental
results and observations. The Modeling Framework for Experimental Physics
describes the process by which physicists revise their models to account for
the newly acquired observations, or change their apparatus to better represent
their models when they encounter discrepancies between actual and expected
behavior of a system. While modeling is a nationally recognized learning
outcome for undergraduate physics lab courses, no assessments of students'
model-based reasoning exist for upper-division labs. As part of a larger effort
to create two assessments of students' modeling abilities, we used the Modeling
Framework to develop and code think-aloud problem-solving activities centered
on investigating an inverting amplifier circuit. This study is the second phase
of a multiphase assessment instrument development process. Here, we focus on
characterizing the range of modeling pathways students employ while
interpreting the output signal of a circuit functioning far outside its
recommended operation range. We end by discussing four outcomes of this work:
(1) Students engaged in all modeling subtasks, and they spent the most time
making measurements, making comparisons, and enacting revisions; (2) Each
subtask occurred in close temporal proximity to all over subtasks; (3)
Sometimes, students propose causes that do not follow logically from observed
discrepancies; (4) Similarly, students often rely on their experiential
knowledge and enact revisions that do not follow logically from articulated
proposed causes.Comment: 18 pages, 5 figure
Longitudinal static optical properties of hydrogen chains: finite field extrapolations of matrix product state calculations
We have implemented the sweep algorithm for the variational optimization of
SU(2) x U(1) (spin and particle number) invariant matrix product states (MPS)
for general spin and particle number invariant fermionic Hamiltonians. This
class includes non-relativistic quantum chemical systems within the
Born-Oppenheimer approximation. High-accuracy ab-initio finite field results of
the longitudinal static polarizabilities and second hyperpolarizabilities of
one-dimensional hydrogen chains are presented. This allows to assess the
performance of other quantum chemical methods. For small basis sets, MPS
calculations in the saturation regime of the optical response properties can be
performed. These results are extrapolated to the thermodynamic limit.Comment: Submitted to J. Chem. Phy
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