Accurate photoionisation cross section for He at non-resonant photon energies

The total single-photon ionisation cross section was calculated for helium atoms in their ground state. Using a full configuration-interaction approach the photoionisation cross section was extracted from the complex-scaled resolvent. In the energy range from ionisation threshold to 59\,eV our results agree with an earlier $B$-spline based calculation in which the continuum is box discretised within a relative error of $0.01\%$ in the non-resonant part of the spectrum. Above the \He^{++} threshold our results agree on the other hand very well to a recent Floquet calculation. Thus our calculation confirms the previously reported deviations from the experimental reference data outside the claimed error estimate. In order to extend the calculated spectrum to very high energies, an analytical hydrogenic-type model tail is introduced that should become asymptotically exact for infinite photon energies. Its universality is investigated considering also H$^-$, Li$^+$, and HeH$^+$. With the aid of the tail corrections to the dipole approximation are estimated.Comment: 20 pages, 7 figures, 2 table

High School Students Embedded in Adult Community College Classes

Early college high schools were established as an initiative of the Bill and Melinda Gates Foundation with the goal for students of earning college credit and an associate degree while in high school. Many of these high school students attend college classes with adults, ages 18 and older, in the same class. Instructors are challenged to address these students’ diverse needs and diverse ways of learning. Young teenagers typically are told exactly what to learn and how it is to be learned; the adult learner, however, is much more independent and he or she learns and thinks differently based on more varied experiences. In this paper, the authors provide some concrete examples of instructional practices based on Knowles’ Model of Adult Learning

Autonomous thruster failure recovery on underactuated spacecraft using model predictive control

Thruster failures historically account for a large percentage of failures that have occurred on orbit. These failures are typically handled through redundancy, however, with the push to using smaller, less expensive satellites in clusters or formations there is a need to perform thruster failure recovery without additional hardware. This means that a thruster failure may cause the spacecraft to become underactuated, requiring more advanced control techniques. A model of a thruster-controlled spacecraft is developed and analyzed with a nonlinear controllability test, highlighting several challenges including coupling, nonlinearities, severe control input saturation, and nonholonomicity. Model Predictive Control (MPC) is proposed as a control technique to solve these challenges. However, the real-time, online implementation of MPC brings about many issues. A method of performing MPC online is described, implemented and tested in simulation as well as in hardware on the Synchronized Position-Hold, Engage, Reorient Experimental Satellites (SPHERES) testbed at the Massachusetts Institute of Technology (MIT) and on the International Space Station (ISS). These results show that MPC provided improved performance over a simple path planning technique

SPHERES flight operations testing and execution

Synchronized Position Hold Engage Reorient Experimental Satellites (SPHERES) is a formation flight testing facility consisting of three satellites operating inside the International Space Station (ISS). The goal is to use the long term microgravity environment of the ISS to mature formation flight and docking algorithms. The operations processes of SPHERES have also matured over the course of the first seven test sessions. This paper describes the evolution of the SPHERES program operations processes from conception to implementation to refinement through flight experience. Modifications to the operations processes were based on experience and feedback from Marshall Space Flight Center Payload Operations Center, USAF Space Test Program office at Johnson Space Center, and the crew of Expedition 13 (first to operate SPHERES on station). Important lessons learned were on aspects such as test session frequency, determination of session success, and contingency operations. This paper describes the tests sessions; then it details the lessons learned, the change in processes, and the impact on the outcome of later test sessions. SPHERES had very successful initial test sessions which allowed for modification and tailoring of the operations processes to streamline the code delivery and to tailor responses based on flight experiences.United States. Dept. of Defense. Space Technologies ProgramUnited States. National Aeronautics and Space Administration. Johnson Space Center ISS Operations TeamUnited States. National Aeronautics and Space Administration. Marshall Space Flight Center Astronaut OfficeUnited States. National Aeronautics and Space Administration. Johnson Space Center Reduced Gravity Offic

Matrix algorithm for solving Schroedinger equations with position-dependent mass or complex optical potentials

We represent low dimensional quantum mechanical Hamiltonians by moderately sized finite matrices that reproduce the lowest O(10) boundstate energies and wave functions to machine precision. The method extends also to Hamiltonians that are neither Hermitian nor PT symmetric and thus allows to investigate whether or not the spectra in such cases are still real. Furthermore, the approach is especially useful for problems in which a position-dependent mass is adopted, for example in effective-mass models in solid-state physics or in the approximate treatment of coupled nuclear motion in molecular physics or quantum chemistry. The performance of the algorithm is demonstrated by considering the inversion motion of different isotopes of ammonia molecules within a position-dependent-mass model and some other examples of one- and two-dimensional Hamiltonians that allow for the comparison to analytical or numerical results in the literature.Comment: 10 pages, 5 figures. Several clarifications in the text and new sect. IV.G. Version to appear in Phys. Rev.

Red-Cockaded Woodpecker Nest-Cavity Selection: Relationships with Cavity Age and Resin Production

ABSTRACT.--We evaluated selection of nest sites by male Red-cockaded Woodpeckers (Picoides borealis) in Texas relative to the age of the cavity when only cavities excavated by the woodpecker were available and when both naturally excavated cavities and artificial cavities we available. We also evaluated nest-cavity selection relative to he ability of naturally excavated cavity trees to produce resin, which is used by the woodpeckers to maintain a barrier against predation by rat snakes (Elaphe spp.), Longleaf pines (Pinus palustris) selected by breeding males as nest trees produced significantly greater resin yields at 2, 8, and 24 h post-wounding than cavity trees used for roosting by other group members. This preference was observed in loblolly pine (P. taeda) and shortleaf pine (P. echinata) cavity trees only at the 2-h resin-sampling period. When only naturally excavated cavities were available. red-cockaded Woodpeckers in both longleaf pine and loblolly-shorleaf pine habitat selected the newest cavities available for their nests sites, possibly as a means to reduce parasites loads. When both naturally excavated and artificial cavity for nesting in loblolly-shortleaf pine habitat, but not in longleaf pine habitat. Resin production in loblolly pine nest trees remained sufficient for continued use, whereas resin production in existing longleaf pine nest trees remained sufficient for continued use, whereas resin production in loblolly pine and shortleaf pine nest trees deceased through time, probably because of woodpecker activity at resin wells. For these latter tree species, breeding males switched to newer cavities and/pr cavity trees with higher resin yields

The Business of Employing People with Disabilities: Four Case Studies

This exploratory study examines employer attitudes towards people with disabilities in the labor market. Through in-depth, semi-structured interviews with senior management, human resources staff, directors of diversity, and hiring managers at four corporations, it pinpoints reasons why businesses chose to hire people with disabilities, investigates the perceived benefits and barriers to hiring people with disabilities, and identifies strategies for successfully hiring and retaining workers with disabilities. It fills a gap in examining the attitudes and decision-making processes of U.S. companies that have been leaders in hiring people with disabilities, as well as delving into the special issues of small businesses that may lack exposure to disability employment. It closes with directions for future studies that could extend our understanding of employment of people with disabilities

Hydrodynamic analog of particle trapping with the Talbot effect

We present the results of an experimental study of the standing waves produced on the surface of a vertically shaken fluid bath just above the Faraday threshold, when a row of equally spaced pillars protrudes from the surface. When the pillar spacing is twice the Faraday wavelength, the resulting wave field is marked by images of the pillars projected at integer multiples of a fixed distance from the row. This projection effect is shown to be analogous to the well-known Talbot or self-imaging effect in optics, and a Faraday-Talbot length is defined that rationalizes the location of the images. A simple model of point sources emitting circular waves captures the observed patterns. We demonstrate that the images may serve as traps for bouncing and walking droplets.National Science Foundation (U.S.) (Grant CMMI-1333242)National Science Foundation (U.S.) (Grant DMS-1614043)Natioanal Science Foundation (U.S.) (Grant CMMI-1727565

Inter- and Intra-rater Reliability of A Grading System for Congenital Diaphragmatic Hernia Defect Size

Background The Congenital Diaphragmatic Hernia Study Group (CDHSG) registry is a multi-institutional tool to track outcomes of patients with CDH. The CDHSG asks surgeons to categorize diaphragmatic defect sizes as type A-D based on published guidelines. The reported size of the defect has been correlated with patient outcomes, but the reliability of this system has never been studied. Our goal was to evaluate the inter- and intra-rater reliability of the CDHSG grading system. Materials and methods Forty-six operative notes from CDH patients that underwent surgical repair at a single institution were collected and cropped to include only the information necessary to grade the hernia defect based on the CDHSG guidelines. The defects were graded by nine pediatric surgeons on two separate occasions (18 wk apart). Inter-rater reliability was calculated using a Cohen's kappa (κ). Intra-rater reliability was calculated using an intraclass correlation coefficient. Results Inter-rater reliability was minimal to weak (κ round1 = 0.395, κ round2 = 0.424). Agreement ranged from 19.57% (κ = −0.0745) to 82.61% (κ = 0.7543). Inter-rater agreement was similar despite operative findings and outcomes: survival yes/no (κ = 0.3690, κ = 0.3518), need for ECMO yes/no (κ = 0.3323, κ = 0.3362), patch repair yes/no (κ = 0.2050, κ = 0.1916), and liver up/down (κ = 0.2941, κ = 0.4404). Intra-rater reliability was good to excellent (intraclass correlation coefficient = 0.88, 95% CI [0.83-0.92]). Agreement with oneself ranged from 71.74% to 93.48%. Conclusions The demonstrated weak inter-rater reliability of the current CDHSG grading system shows the need for improvement in how the grading system is applied by surgeons when reporting CDH defect size