Comparison of Design Approaches for Low-Cost Sampling Mechanisms in Open-Source Chemical Instrumentation

Robotic positioning systems are used in a variety of chemical instruments, primarily for liquid handling purposes, such as autosamplers from vials or well plates. Here, two approaches to the design of open-source autosampler positioning systems for use with 96-well plates are described and compared. The first system, a 3-axis design similar to many low-cost 3D printers that are available on the market, is constructed using an aluminum frame and stepper motors. The other system relies upon a series of 3D printed parts to achieve movement with a series of linker arms based on Selective Compliance Assembly Robot Arm (SCARA) design principles. Full printer design files, assembly instructions, software, and user directions are included for both samplers. The positioning precision of the 3-axis system is better than the SCARA mechanism due to finer motor control, albeit with a slightly higher cost of materials. Based on the improved precision of this approach, the 3-axis autosampler system was used to demonstrate the generation of a segmented flow droplet stream from adjacent wells within a 96-well plate

Characterizing Multi-planet Systems with Classical Secular Theory

Classical secular theory can be a powerful tool to describe the qualitative character of multi-planet systems and offer insight into their histories. The eigenmodes of the secular behavior, rather than current orbital elements, can help identify tidal effects, early planet-planet scattering, and dynamical coupling among the planets, for systems in which mean-motion resonances do not play a role. Although tidal damping can result in aligned major axes after all but one eigenmode have damped away, such alignment may simply be fortuitous. An example of this is 55 Cancri (orbital solution of Fischer et al., 2008) where multiple eigenmodes remain undamped. Various solutions for 55 Cancri are compared, showing differing dynamical groupings, with implications for the coupling of eccentricities and for the partitioning of damping among the planets. Solutions for orbits that include expectations of past tidal evolution with observational data, must take into account which eigenmodes should be damped, rather than expecting particular eccentricities to be near zero. Classical secular theory is only accurate for low eccentricity values, but comparison with other results suggests that it can yield useful qualitative descriptions of behavior even for moderately large eccentricity values, and may have advantages for revealing underlying physical processes and, as large numbers of new systems are discovered, for triage to identify where more comprehensive dynamical studies should have priority.Comment: Published in Celestial Mechanics and Dynamical Astronomy, 25 pages, 10 figure

A Kinematic Model to Predict a Continuous Range of Human-Like Walking Speed Transitions

While constant speed gait is well understood, far less is known about how humans change walking speed. It is also unknown if the transition steps smoothly morph between speeds, or if they are unique. Using data from a prior study in which subjects transitioned between five speeds while walking on a treadmill, joint kinematic data were decomposed into trend and periodic components. The trend captured the time-varying nature of the gait, and the periodic component captured the cyclic nature of a stride. The start and end of the transition were found by detecting where the trend diverged from a &#x00B1;2 standard deviation band around the mean of the pre- and post-transition trend. On average, the transition started within half a step of when the treadmill changed speed ( ${p\ll {0}.{001}}$ for equivalence test). The transition length was 2 to 3 steps long. A predictive kinematic model was fit to the experimental data using Bezier polynomials for the trend and Fourier series for the periodic component. The model was fit using 1) only constant speed walking, 2) only speed transition steps, and 3) a random sample of five step types and then validated using the complement of the training data. Regardless of the training set, the model accurately predicted untrained gaits (normalized RMSE { < {0}.{4} \approx {2}^{\circ} } , normalized maximum error generally { < {1}.{5} \approx {7}.{5}^{\circ} } ). Because the errors were similar for all training sets, this implies that joint kinematics smoothly morph between gaits when humans change speed

Teaching college students communication strategies for effective social justice advocacy /

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