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Human ambulation is typically characterized during steady-state isolated tasks (e.g., walking, running, stair ambulation). However, general human locomotion comprises continuous adaptation to the varied terrains encountered during activities of daily life. To fill an important gap in knowledge that may lead to improved therapeutic and device interventions for mobility-impaired individuals, it is vital to identify how the mechanics of individuals change as they transition between different ambulatory tasks, and as they encounter terrains of differing severity. In this work, we study lower-limb joint kinematics during the transitions between level walking and stair ascent and descent over a range of stair inclination angles. Using statistical parametric mapping, we identify where and when the kinematics of transitions are unique from the adjacent steady-state tasks. Results show unique transition kinematics primarily in the swing phase, which are sensitive to stair inclination. We also train Gaussian process regression models for each joint to predict joint angles given the gait phase, stair inclination, and ambulation context (transition type, ascent/descent), demonstrating a mathematical modeling approach that successfully incorporates terrain transitions and severity. The results of this work further our understanding of transitory human biomechanics and motivate the incorporation of transition-specific control models into mobility-assistive technology.

 

Modern short-range gravity experiments that seek to test the Newtonian inverse-square law or weak equivalence principle of general relativity typically involve measuring the minute variations in the twist angle of a torsion pendulum. Motivated by various theoretical arguments, recent efforts largely focus on measurements with test mass separations in the sub-millimeter regime. To measure the twist, many experiments employ an optical autocollimator with a noise performance of ∼300 nrad[Formula: see text] in the 0.1–10 mHz band, enabling a measurement uncertainty of a few nanoradians in a typical integration time. We investigated an alternative method for measuring a small twist angle through the construction of a modified Michelson interferometer. The main modification is the introduction of two additional arms that allow for improved angular alignment. A series of detectors and LabView software routines were developed to determine the orientation of a mirror attached to a sinusoidally driven rotation stage that oscillated with an amplitude of 0.35 mrad and a period of 200 s. In these measurements, the resolution of the interferometer is 8.1  μrad per fringe, while its dynamic range spanned 0.962 mrad. We compare the performance of this interferometric optical system to existing autocollimator-based methods, discussing its implementation, possible advantages, and future potential, as well as disadvantages and limitations. 

In this research paper, we describe faculty development as mentors to postdoctoral fellows (postdocs). Postdoctoral fellowships have become a significant step in academic and industry positions, while little research investigates the purpose of a postdoc position, the experiences of postdocs, and how faculty develop as postdoc advisors. As part of a larger project investigating postdoc mentorship, nineteen semi-structured qualitative interviews with faculty advisors uncovered themes about how postdoc advisors learn to mentor and advise postdocs. Faculty from U.S. and Canadian universities completed 60-minute online interviews. Participants had varying experience and expertise in advising postdocs. Observational learning theory provides a framework for identifying the process of learning from observation and the replication of mentors’ past experiences. Open and axial coding was used to identify faculty experiences that informed how they mentored their postdoctoral fellows. Faculty who had completed a postdoc as part of their training reflected on their experiences, often identifying positive and negative experiences they used to guide, mentor, and plan the development of the postdocs they advise. Faculty who did not complete a postdoc used doctoral and industry experiences to inform their decisions. This work provides a unique window into postdoctoral training and 

Postdoctoral fellows report experiencing misalignment between their expectations and their experiences in postdoctoral training. Little research explores their experiences with less still attempting to identify advisors’ expectations of postdoctoral fellows. This research aims to describe the knowledge, skills, and attributes (KSA) advisors/principal investigators expect when postdoctoral fellows begin and the expectations for developing postdoc KSA during the fellowship. Qualitative semi-structured interviews with postdoctoral advisors provide data about the hiring, starting, and development expectations advisors have for postdocs. Axial coding with KSA and abductive analysis identify advisors’ KSA expectations. Postdoctoral advisors describe hiring requirements and development expectations that do not clearly align. This misalignment starts postdocs and advisors in a new relationship with already misaligned expectations. Clarified language in hiring requirements and development expectations can help advisors and postdocs begin the fellowship with better-aligned expectations. The research reported here provides language to advisors and postdocs to assist and guide KSA expectations. 

We describe a liquid-cryogen free cryostat with ultra-low vibration levels, which allows for continuous operation of a torsion balance at cryogenic temperatures. The apparatus uses a commercially available two-stage pulse-tube cooler and passive vibration isolation. The torsion balance exhibits torque noise levels lower than room temperature thermal noise by a factor of about four in the frequency range of 3–10 mHz, limited by residual seismic motion and by radiative heating of the pendulum body. In addition to lowering thermal noise below room-temperature limits, the low-temperature environment enables novel torsion balance experiments. Currently, the maximum duration of a continuous measurement run is limited by accumulation of cryogenic surface contamination on the optical elements inside the cryostat.