Orbits in Extended Mass Distributions: General Results and the Spirographic Approximation

This paper explores orbits in extended mass distributions and develops an analytic approximation scheme based on epicycloids (spirograph patterns). We focus on the Hernquist potential which provides a good model for many astrophysical systems, including elliptical galaxies, dark matter halos, and young embedded star clusters. For a given potential, one can readily calculate orbital solutions as a function of energy and angular momentum using numerical methods. In contrast, this paper presents a number of analytic results for the Hernquist potential and proves a series of general constraints showing that orbits have similar properties for any extended mass distribution (including, e.g., the NFW profile). We discuss circular orbits, radial orbits, zero energy orbits, different definitions of eccentricity, analogs of Kepler's law, the definition of orbital elements, and the relation of these orbits to spirograph patterns (epicycloids). Over much of parameter space the orbits can be adequately described (with accuracy better than 10%) using the parametric equations of epicycloids, thereby providing an analytic description of the orbits. As an application of this formal development, we find a solution for the orbit of the Large Magellanic Cloud in the potential of our Galaxy.Comment: 40 pages including 9 figures; accepted to The Astrophysical Journa

Indices from flow-volume curves in relation to cephalometric, ENT- and sleep-O2 saturation variables in snorers with and without obstructive sleep-apnoea

In a group of 37 heavy snorers with obstructive sleep apnoea (OSA, Group 1) and a group of 23 heavy snorers without OSA (Group 2) cephalometric indices, ENT indices related to upper airway collapsibility, and nocturnal O2 desaturation indices were related to variables from maximal expiratory and inspiratory flow-volume (MEFV and MIFV) curves. The cephalometric indices used were the length and diameter of the soft palate (spl and spd), the shortest distance between the mandibular plane and the hyoid bone (mph) and the posterior airway space (pas). Collapsibility of the upper airways was observed at the level of the tongue base and soft palate by fibroscopy during a Muller manoeuvre (mtb and msp) and ranked on a five point scale. Sleep indices measured were the mean number of oxygen desaturations of more than 3% per hour preceded by an apnoea or hypopnoea of more than 10 s (desaturation index), maximal sleep oxygen desaturation, baseline arterial oxygen saturation (Sa,O2) and, in the OSA group, percentage of sleep time with Sa,O2 < 90%. The variables obtained from the flow-volume curves were the forced vital capacity (FVC), forced expiratory and inspiratory volume in 1 s (FEV1 and FIV1), peak expiratory and peak inspiratory flows (PEF and PIF), and maximal flow after expiring 50% of the FVC (MEF50). The mean of the flow-volume variables, influenced by upper airway aperture (PEF, FIV1) was significantly greater than predicted.(ABSTRACT TRUNCATED AT 250 WORDS

Aerospace Medicine and Biology: A continuing bibliography with indexes (supplement 133)

This special bibliography lists 276 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System in September 1974

DEVELOPMENT OF A DYNAMIC BALLOON VOLUME SENSOR SYSTEM FOR USE IN PULSATING BALLOON CATHETERS WITH CHANGING HELIUM CONCENTRATIONS

A dynamic balloon volume sensor system (DBVSS) was designed for use with the intra-aortic balloon pump (IABP), a therapeutic device to assist heart recovery after cardiac dysfunction or cardiac trauma, and the Pittsburgh respiratory support catheter (RSC), an internally deployed gas exchange device which augments lung function. The DBVSS was designed to detect the degree of inflation of the balloons incorporated into each device as they pulse within a patient. Both devices require full inflation for optimal performance, and both will under-inflate during normal operation. The sensor system requirements were to measure volumes within 10% of the actual across the range of expected pulsation frequencies as well as in changing concentrations of helium.The DBVSS employed a hot wire anemometer to detect the flow entering the balloon, combined with a computer algorithm to integrate the flow to find volume. The system compensated for the flow reading changes resulting from changing helium concentration by measuring gas properties during zero gas flow between pulsations, and used this data to correct the flow profile at each helium concentration. The volume from the DBVSS was compared to the volume standard as measured by water displacement in a plethysmograph.The system was able to accurately measure delivered balloon volume under changing gas composition as well as detected volume loss from the balloon across helium concentrations. The DBVSS measured the volume within 10% across these tests, as well as under compression of the balloon, high resistance in the driveline and across frequencies up to 480 beats per minute. The DBVSS was proved to be within the design requirements for helium concentration and inflation methods for both the devices considered