The Soft Landing Problem: Minimizing Energy Loss by a Legged Robot Impacting Yielding Terrain

Enabling robots to walk and run on yielding terrain is increasingly vital to endeavors ranging from disaster response to extraterrestrial exploration. While dynamic legged locomotion on rigid ground is challenging enough, yielding terrain presents additional challenges such as permanent ground deformation which dissipates energy. In this paper, we examine the soft landing problem: given some impact momentum, bring the robot to rest while minimizing foot penetration depth. To gain insight into properties of penetration depth-minimizing control policies, we formulate a constrained optimal control problem and obtain a bang-bang open-loop force profile. Motivated by examples from biology and recent advances in legged robotics, we also examine impedance-control solutions to the dimensionless soft landing problem. Through simulations, we find that optimal impedance reduces penetration depth nearly as much as the open-loop force profile, while remaining robust to model uncertainty. Through simulations and experiments, we find that the solution space is rich, exhibiting qualitatively different relationships between impact velocity and the optimal impedance for small and large dimensionless impact velocities. Lastly, we discuss the relevance of this work to minimum-cost-of-transport locomotion for several actuator design choices

The Cvt pathway as a model for selective autophagy

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/116339/1/feb2s0014579310001079.pd

Efficient, Responsive, and Robust Hopping on Deformable Terrain

Legged robot locomotion is hindered by a mismatch between applications where legs can outperform wheels or treads, most of which feature deformable substrates, and existing tools for planning and control, most of which assume flat, rigid substrates. In this study we focus on the ramifications of plastic terrain deformation on the hop-to-hop energy dynamics of a spring-legged monopedal hopping robot animated by a switched-compliance energy injection controller. From this deliberately simple robot-terrain model, we derive a hop-to-hop energy return map, and we use physical experiments and simulations to validate the hop-to-hop energy map for a real robot hopping on a real deformable substrate. The dynamical properties (fixed points, eigenvalues, basins of attraction) of this map provide insights into efficient, responsive, and robust locomotion on deformable terrain. Specifically, we identify constant-fixed-point surfaces in a controller parameter space that suggest it is possible to tune control parameters for efficiency or responsiveness while targeting a desired gait energy level. We also identify conditions under which fixed points of the energy map are globally stable, and we further characterize the basins of attraction of fixed points when these conditions are not satisfied. We conclude by discussing the implications of this hop-to-hop energy map for planning, control, and estimation for efficient, agile, and robust legged locomotion on deformable terrain.Comment: 17 pages, 13 figures, submitted to IEEE Transactions on Robotic

Residential radon exposure and lung cancer: variation in risk estimates using alternative exposure scenarios

The most direct way to derive risk estimates for residential radon progeny exposure is through epidemiologic studies that examine the association between residential radon exposure and lung cancer. However, the National Research Council concluded that the inconsistency among prior residential radon case-control studies was largely a consequence of errors in radon dosimetry. This paper examines the impact of applying various epidemiologic dosimetry models for radon exposure assessment using a common data set from the Iowa Radon Lung Cancer Study (IRLCS). The IRLCS uniquely combined enhanced dosimetric techniques, individual mobility assessment, and expert histologic review to examine the relationship between cumulative radon exposure, smoking, and lung cancer. The a priori defined IRLCS radon-exposure model produced higher odds ratios than those methodologies that did not link the subject\u27s retrospective mobility with multiple, spatially diverse radon concentrations. In addition, the smallest measurement errors were noted for the IRLCS exposure model. Risk estimates based solely on basement radon measurements generally exhibited the lowest risk estimates and the greatest measurement error. The findings indicate that the power of an epidemiologic study to detect an excess risk from residential radon exposure is enhanced by linking spatially disparate radon concentrations with the subject\u27s retrospective mobility

Novel magneto-optic behaviour from a polysquaraine

Copyright © 2013 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Synthetic Metals. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Synthetic Metals, Volume 171 (1 May 2013), DOI: 10.1016/j.synthmet.2013.03.010We report that poly((2,5-bis(1-methylpyrrol-2-yl)thiophene)squaraine) can be synthesized as a dark green insoluble powder which when subjected to shear force and pressed as a disk exhibits a gold-green near optical quality surface with semi-metallic behaviour. Reflectivity measurements at a wavelength of 819 nm reveal a high (72°) pseudo-Brewster angle and non-zero p-reflectivity whilst electrical measurements using a four-point probe return a conductivity of 1 × 10−5 S cm−1. Unexpectedly the disks also exhibit magneto-optic (MO) activity which it appears must arise from a weak magnetic component intrinsic to the samples. In both the longitudinal and transverse Kerr configurations large fractional changes in reflectivity (ΔI/I ≈ 2.5 × 10−2) are observed across a wide range of angles of incidence for wavelengths between 400 nm and 1064 nm on application and reversal of a magnetic field. Anomalously for these configurations all the MO effects observed are quadratic in the applied field and no first-order effects linear in applied field are observed for any state of incident polarisation. Examined using conventional magnetometry, disk samples return saturation magnetization values of 4.13 × 10−3 emu g−1 on a vibrating sample magnetometer and smaller samples similarly processed and prepared for examination by Squid magnetometer confirmatory values of 4.9 × 10−3 emu g−1. Magnetization curves from both instruments have a similar form, saturating at about 1.14 kOe, and are also in close correspondence with curves derived by plotting the magneto-optic signal as a function of field after allowance for the quadratic nature of the observed MO response. Similarly, both the magnetic and magneto-optic behaviour of all samples is isotropic in plane. Taken together, all experimental observations on this fully organic polymer appear, surprisingly, to be commensurate with the development at room temperature of some form of magnetic state throughout very limited regions of the material. A very tentative model able to reconcile the magnetic and MO observations on the supposition that the magnetic state may be of a reduced dimensional nature is presented. We are very aware that the appearance of an intrinsic room temperature magnetism in the material studied is highly unlikely and that this interpretation of the results presented is strongly dependent on using MO evidence to support chemical analysis, which included multi-elements scans on an ICP and ESR, in precluding contamination

Preservation of information in a prebiotic package model

The coexistence between different informational molecules has been the preferred mode to circumvent the limitation posed by imperfect replication on the amount of information stored by each of these molecules. Here we reexamine a classic package model in which distinct information carriers or templates are forced to coexist within vesicles, which in turn can proliferate freely through binary division. The combined dynamics of vesicles and templates is described by a multitype branching process which allows us to write equations for the average number of the different types of vesicles as well as for their extinction probabilities. The threshold phenomenon associated to the extinction of the vesicle population is studied quantitatively using finite-size scaling techniques. We conclude that the resultant coexistence is too frail in the presence of parasites and so confinement of templates in vesicles without an explicit mechanism of cooperation does not resolve the information crisis of prebiotic evolution.Comment: 9 pages, 8 figures, accepted version, to be published in PR

Mechanisms regulating large-scale seasonal fluctuations in Alexandrium fundyense populations in the Gulf of Maine : results from a physical–biological model

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B. V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 52 (2005): 2698-2714, doi:10.1016/j.dsr2.2005.06.021.Observations of Alexandrium fundyense in the Gulf of Maine indicate several salient characteristics of the vegetative cell distributions: patterns of abundance are gulf-wide in geographic scope; their main features occur in association with the Maine Coastal Current; and the center of mass of the distribution shifts upstream from west to east during the growing season from April to August. The mechanisms underlying these aspects are investigated using coupled physical-biological simulations that represent the population dynamics of A. fundyense within the seasonal mean flow. A model that includes germination, growth, mortality, and nutrient limitation is qualitatively consistent with the observations. Germination from resting cysts appears to be a key aspect of the population dynamics that confines the cell distribution near the coastal margin, as simulations based on a uniform initial inoculum of vegetative cells across the Gulf of Maine produces blooms that are broader in geographic extent than is observed. In general, cells germinated from the major cyst beds (in the Bay of Fundy and near Penobscot and Casco Bays) are advected in the alongshore direction from east to west in the coastal current. Growth of the vegetative cells is limited primarily by temperature from April through June throughout the gulf, whereas nutrient limitation occurs in July and August in the western gulf. Thus the seasonal shift in the center of mass of cells from west to east can be explained by changing growth conditions: growth is more rapid in the western gulf early in the season due to warmer temperatures, whereas growth is more rapid in the eastern gulf later in the season due to severe nutrient limitation in the western gulf during that time period. A simple model of encystment based on nutrient limitation predicts deposition of new cysts in the vicinity of the observed cyst bed offshore of Casco and Penobscot Bays, suggesting a pathway of re-seeding the bed from cells advected downstream in the coastal current. A retentive gyre at the mouth of the Bay of Fundy tends to favor re-seeding that cyst bed from local populations.We gratefully acknowledge the support of the US ECOHAB Program, sponsored by NOAA, NSF, EPA, NASA, and ONR

Mindfulness meditation targets transdiagnostic symptoms implicated in stress-related disorders: Understanding relationships between changes in mindfulness, sleep quality, and physical symptoms

Mindfulness-Based Stress Reduction (MBSR) is an 8-week meditation program known to improve anxiety, depression, and psychological well-being. Other health-related effects, such as sleep quality, are less well established, as are the psychological processes associated with therapeutic change. This prospective, observational study (n=213) aimed to determine whether perseverative cognition, indicated by rumination and intrusive thoughts, and emotion regulation, measured by avoidance, thought suppression, emotion suppression, and cognitive reappraisal, partly accounted for the hypothesized relationship between changes in mindfulness and two health-related outcomes: sleep quality and stress-related physical symptoms. As expected, increased mindfulness following the MBSR program was directly correlated with decreased sleep disturbance (r=-0.21, p=0.004) and decreased stress-related physical symptoms (r=-0.38, p<0.001). Partial correlations revealed that pre-post changes in rumination, unwanted intrusive thoughts, thought suppression, experiential avoidance, emotion suppression, and cognitive reappraisal each uniquely accounted for up to 32% of the correlation between the change in mindfulness and change in sleep disturbance and up to 30% of the correlation between the change in mindfulness and change in stress-related physical symptoms. Results suggest that the stress-reducing effects of MBSR are due, in part, to improvements in perseverative cognition and emotion regulation, two “transdiagnostic” mental processes that cut across stress-related disorders

Conference on the Federal Sentencing Guidelines, Panel 3: The Allocation of Discretion Under the Guidelines

The guidelines have shifted the locus of discretion from the judge to the prosecutor. This transfer has drastically changed sentencing because the prosecutor\u27s role is very different from the judge\u27s role. Before the guidelines, the prosecutor\u27s role in sentencing was minimal. The prosecutor could put a cap on the sentence by accepting a plea to a charge with a low maximum, but there was virtually no instance in which the charge would put a floor under the judge\u27s sentence. The judge, on the other hand, could sentence however he liked. Not only was the judge\u27s decision correct because it was final – there was no appellate review of sentences within the statutory maximum – it was correct because there was no law by which it could be called incorrect. Absent a few factors that were statutorily excluded from consideration, the judge could take into account any factor he thought relevant, and weigh it to whatever degree he thought it counted. The judge could be harsh or lenient, a retributivist or a utilitarian, a believer in deterrence or rehabilitation