Radial velocities of fifteen double-mode bulge RR Lyrae (RR01) stars are presented, six of which belong to a compact group of RR01 stars in pulsation space, with the ratio of first-overtone period to fundamental-mode period, P f o /P f ∼0.74, and P f ∼0.44. It has been suggested that these pulsationally clumped RR01 stars are a relic of a disrupted dwarf galaxy or stellar cluster, as they also appear to be spatially coherent in a vertical strip across the bulge. However, the radial velocities of the stars presented here, along with proper motions from Gaia DR2, show a large range of radial velocities, proper motions and distances for the bulge RR01 stars in the pulsation clump, much larger than the RR01 stars in the Sagittarius dwarf galaxy (Sgr). Therefore, in contrast to the kinematics of the RRL stars belonging to Sgr, and those in and surrounding the bulge globular cluster NGC 6441, there is no obvious kinematic signature within the pulsationally clumped RR01 stars. If the pulsationally clumped RR01 stars belonged to the same system in the past and were accreted, their accretion in the inner Galaxy was not recent, as the kinematic signature of this group has been lost (i.e., these stars are now well-mixed within the inner Galaxy). We show that the apparent spatial coherence reported for these stars could have been caused by small number statistics. The orbits of the RR01 stars in the inner Galaxy suggest they are confined to the innermost ∼4 kpc of the Milky Way.

People with disabilities often struggle with mobility issues, so there is a strong desire for devices such as powerchairs, which can provide more freedom. Currently, wheelchair demand in the US is increasing due to an upsurge in the elderly population. Often electric powerchairs suitable for outdoor use are extremely expensive, cannot be used indoors, and are not covered by medical insurance. In this project, these problems are addressed through the design of a chair which is suitable for both rough outdoor terrain and indoor use. This project is based on a request for a powerchair which our client’s son, who has cerebral palsy, can use on family trips in outdoor environments including grass, gravel, and sand. A photo of a previous nonfunctional prototype was provided to the team as a reference, and a full redesign was performed to resolve the problems identified. Before proceeding with the design, various sources were consulted to gain a thorough understanding of currently available technology and design methods. Many different adjustment methods and features were considered, including an adjustable frame, tracks, and a lifting system for curb mounting. The overall design selected is a welded sheet metal frame with wheels, and it was determined that the chair should have an adjustable wheelbase width to provide both outdoor stability and indoor maneuverability. Key considerations for the design include battery life, motor torque, maximum load, seat size, door width, and cost. The final specifications are based on the needs of the client, Kevin Sample, as well as an analysis of the wider consumer market. The width adjustment design uses an axle above the driving wheels, which are connected to it by sliding sleeves. Automatic adjustment is accomplished using a linear actuator. The drive wheels are large and run at low pressure to surmount obstacles and damp vibrations. Differential steering combined with rear caster wheels gives the chair a small turning radius, and its length is comparable to that of standard manual wheelchairs. The seat can be easily removed to access the battery and control system or to load the chair into a vehicle. A joystick is used to control the speed and direction of the chair, while a separate momentary switch is used for the linear actuator. Throughout the modeling process, stress analysis was performed using simulations in Inventor. Any necessary adjustments were made to ensure that none of the parts will fail, considering both failure theory and fatigue. Various grades of aluminum were selected for the majority of the manufactured parts, due to their corrosion resistance and light weight. The device is currently in the prototype manufacturing stage. If it is later marketed, a curb mounting device may also be included; this was decided against mainly due to cost and time restrictions. Space has also been left for a carrying basket, which will likely be added to the first prototype. The initial goal is to produce a single chair for our client, although the design may later be submitted for Medicare and ADA approval.

No abstract