Unraveling the Helix Nebula: Its Structure and Knots

Through HST imaging of the inner part of the main-ring of the Helix Nebula together with CTIO 4-m images of the fainter outer parts, we have an unprecedented-quality view of the nearest bright planetary nebula. These images have allowed determination that the main-ring of the nebula is composed of an inner-disk of about 499\arcsec diameter (0.52 pc) surrounded by an outer-ring (in reality a torus) of 742\arcsec diameter (0.77 pc) whose plane is highly inclined to the plane of the disk. This outer-ring is surrounded by an outermost-ring of 1500\arcsec (1.76 pc) diameter which is flattened on the side colliding with the ambient interstellar medium. The inner-disk has an extended distribution of low density gas along its rotational axis of symmetry and the disk is optically thick to ionizing radiation, as is the outer-ring. Published radial velocities of the knots provides support for the two-component structure of the main-ring of the nebula and to the idea that the knots found there are expanding along with the nebular material from which it recently originated. There is a change in the morphology of the knots as a function of the distance from the local ionization front. This supports a scenario in which the knots are formed in or near the ionization front and are then sculpted by the stellar radiation from the central star as the ionization front advances beyond them.Comment: 30 pages, 20 figures, many figures have reduce fidelity for astroph preprint. Note: URLs in preprint were change

Effects of Wearing an ACL Brace on Hamstring and Quadriceps Muscle Activity When Performing a Body Weight Squat

After surgical repair of the anterior cruciate ligament (ACL) a functional knee brace is used to support the injured knee. Of importance, would be the reduction of actions that would promote anterior tibial translation relative to the femur. PURPOSE: The purpose of this study was to determine if the use of a functional ACL brace proportionally reduces quadriceps relative to hamstring muscle activity during a body weight squat. METHODS: Seven collegiate athletes (20.5±1.0 yrs, 183.9±9.58 cm and 91.77±11.95 kg) provided informed consent and participated in this study. Two gel bipolar surface Ag-AgCl electrodes were placed on each of the muscle bellies of the vastus lateralis (VL) and the biceps femoris (BF) of the dominant leg. Participants performed eight repetitions of a two-legged bodyweight squat with and without a functional knee brace at a cadence of 54 bpm. RMS EMG was computed across a 200 ms window and analyzed for the middle six repetitions at 45° and 60° of knee flexion during the movement. EMG data were collected at 1000Hz and normalized to the respective maximum voluntary isometric contraction (MVIC) for each muscle. Hamstrings and quadriceps activity for the upward phase of movement were evaluated separately, with two 2x2 (Muscle x Brace Condition) repeated measures ANOVAs. RESULTS: No interaction between muscle and brace condition was observed at 45° (F(1,6) = 5.369, p = 0.06) or 60° (F(1,6) = 5.241 p = 0.062). At 45° and 60° quadriceps activity tended to increase and hamstrings activity tended to decrease when wearing the brace (Table 1) but these differences were not significant (F(1,6)=2.54, p=0.16; F(1,6)=2.90, p=0.14, respectively). CONCLUSION: The trend in muscle activity surprisingly suggests that the movement was more quadriceps dominant while wearing the brace. The quadriceps group had 4.6x and 1.7x more muscle activity than the hamstring during the braced squat and non-braced squat respectively. This data suggests that after the initial healing period, when rehabilitating an ACL injury the functional brace should be used sparingly so the hamstrings may be adequately strengthened

Developing autonomous learning in first year university students using perspectives from positive psychology

Autonomous learning is a commonly occurring learning outcome from university study, and it is argued that students require confidence in their own abilities to achieve this. Using approaches from positive psychology, this study aimed to develop confidence in first‐year university students to facilitate autonomous learning. Psychological character strengths were assessed in 214 students on day one at university. Two weeks later their top three strengths were given to them in study skills modules as part of a psycho‐educational intervention designed to increase their self‐efficacy and self‐esteem. The impact of the intervention was assessed against a control group of 40 students who had not received the intervention. The results suggested that students were more confident after the intervention, and that levels of autonomous learning increased significantly compared to the controls. Character strengths were found to be associated with self‐efficacy, self‐esteem and autonomous learning in ways that were theoretically meaningful

Contamination control engineering design guidelines for the aerospace community

Thermal control surfaces, solar arrays, and optical devices may be adversely affected by a small quantity of molecular and/or particulate contamination. What is rarely discussed is how one: (1) quantifies the level of contamination that must be maintained in order for the system to function properly, and (2) enforces contamination control to ensure compliance with requirements. This document is designed to address these specific issues and is intended to serve as a handbook on contamination control for the reader, illustrating process and methodology while providing direction to more detailed references when needed. The effects of molecular contamination on reflecting and transmitting surfaces are examined and quantified in accordance with MIL STD 1246C. The generation, transportation, and deposition of molecular contamination is reviewed and specific examples are worked to illustrate the process a design engineer can use to estimate end of life cleanliness levels required by solar arrays, thermal control surfaces, and optical surfaces. A similar process is used to describe the effect of particulate contamination as related to percent area coverage (PAC) and bi-directional reflectance distribution function (BRDF). Relationships between PAC and surface cleanliness, which include the effects of submicron sized particles, are developed and BRDF is related to specific sensor design parameters such as Point Source Transmittance (PST). The pros and cons of various methods of preventing, monitoring, and cleaning surfaces are examined and discussed

Properties of 3-manifolds for relativists

In canonical quantum gravity certain topological properties of 3-manifolds are of interest. This article gives an account of those properties which have so far received sufficient attention, especially those concerning the diffeomorphism groups of 3-manifolds. We give a summary of these properties and list some old and new results concerning them. The appendix contains a discussion of the group of large diffeomorphisms of the $l$-handle 3-manifold.Comment: 20 pages. Plain-TeX, no figures, 1 Table (A4 format

A Model of Basic Surgical Skills Course to Supplement the Training of Foundation-Year Doctors by Efficient Use of Local Resources

INTRODUCTION: This study investigates the efficiency of teaching basic surgical skills to foundation-year doctors and medical students by using local resources. METHODS: A course comprising 4 workshops, once a week, of 3 hours duration per session was delivered using local education center facilities and using the local faculty of consultants and surgical trainees. Teaching methods include practical skill stations supplemented with short didactic lectures and group discussion. Precourse and postcourse assessments were completed by candidates and analyzed to measure outcomes of the course both subjectively and objectively. RESULTS: A total number of 20 participants completed the course. On completion of the course, (1) participants' theoretical knowledge improved significantly (p < 0.0001), as measured by multiple-choice questions, and scores improved by 35% (mean 44%, standard deviation = 16%) before the course compared to (mean = 79%, standard deviation = 13) after the course; (2) the level of confidence in knowledge and skills was measured by a questionnaire on a scale of 1 to 5, and there was a significant (p < 0.0001) improvement on postcourse assessment (mean difference = 1.5, 95% CI: 0.7-2.4); and (3) practical skills such as suture position, knot tying, and wound apposition significantly improved after the course, χ(2) (2) = 16, p < 0.001; χ(2) (2) = 18, p < 0.001; and χ(2) (2) = 22, p < 0.0001, respectively. CONCLUSION: Effective delivery of basic surgical skills to foundation-year doctors by using local resources can be achieved at low cost