Paleolakes and life on early Mars

Two distinct directions have begun to elucidate key parameters in the search for extinct life on Mars. Carbonate sediments, deposited about 10,000 years ago in association with biological activity, have been sampled from the paleolake beds of Lake Vanda and Meirs in the McMurdo Dry Valleys in Antarctica. These samples are being analyzed for simple biological signatures that remain in cold and dry paleolake sediments, namely microfossils, percent carbonate, and total organic carbon. Our second initiative is the study of Colour Lake, in the Canadian Arctic, that periodically maintains a perennial ice cover. Physical measurements started this year will be used to determine one end point for ice covered lake environments and will be compared to continuous measurements from Antarctic lakes started in November 1985. Interestingly, Colour Lake also supports benthic mat communities, but the low pH precludes carbonate deposition. This research will broaden our knowledge base for what conditions are necessary for ice covered lake formation and what biological signatures will remain in paleolake deposits

Extension of the sun-synchronous Orbit

Through careful consideration of the orbit perturbation force due to the oblate nature of the primary body a secular variation of the ascending node angle of a near-polar orbit can be induced without expulsion of propellant. Resultantly, the orbit perturbations can be used to maintain the orbit plane in, for example, a near-perpendicular (or at any other angle) alignment to the Sun-line throughout the full year of the primary body; such orbits are normally termed Sun-synchronous orbits [1, 2]. Sun-synchronous orbits about the Earth are typically near-circular Low-Earth Orbits (LEOs), with an altitude of less than 1500 km. It is normal to design a LEO such that the orbit period is synchronised with the rotation of the Earth‟s surface over a given period, such that a repeating ground-track is established. A repeating ground-track, together with the near-constant illumination conditions of the ground-track when observed from a Sun-synchronous orbit, enables repeat observations of a target over an extended period under similar illumination conditions [1, 2]. For this reason, Sun-synchronous orbits are extensively used by Earth Observation (EO) platforms, including currently the Environmental Satellite (ENVISAT), the second European Remote Sensing satellite (ERS-2) and many more. By definition, a given Sun-synchronous orbit is a finite resource similar to a geostationary orbit. A typical characterising parameter of a Sun-synchronous orbit is the Mean Local Solar Time (MLST) at descending node, with a value of 1030 hours typical. Note that ERS-1 and ERS-2 used a MLST at descending node of 1030 hours ± 5 minutes, while ENVISAT uses a 1000 hours ± 5 minutes MLST at descending node [3]. Following selection of the MLST at descending node and for a given desired repeat ground-track, the orbit period and hence the semi-major axis are fixed, thereafter assuming a circular orbit is desired it is found that only a single orbit inclination will enable a Sun-synchronous orbit [2]. As such, only a few spacecraft can populate a given repeat ground-track Sun-synchronous orbit without compromise, for example on the MLST at descending node. Indeed a notable feature of on-going studies by the ENVISAT Post launch Support Office is the desire to ensure sufficient propellant remains at end-of-mission for re-orbiting to a graveyard orbit to ensure the orbital slot is available for future missions [4]. An extension to the Sun-synchronous orbit is considered using an undefined, non-orientation constrained, low-thrust propulsion system. Initially the low-thrust propulsion system will be considered for the free selection of orbit inclination and altitude while maintaining the Sun-synchronous condition. Subsequently the maintenance of a given Sun-synchronous repeat-ground track will be considered, using the low-thrust propulsion system to enable the free selection of orbit altitude. An analytical expression will be developed to describe these extensions prior to then validating the analytical expressions within a numerical simulation of a spacecraft orbit. Finally, an analysis will be presented on transfer and injection trajectories to these orbits

Inclusive Scholarship: Developing Black Studies in the United States

Brings together four reports commissioned between 1982 and 2000 that examine the history of African American Studies, its impact, and its institutionalization. Reviews Ford's grantmaking to African American Studies programs from 1982 to 2007

Accurate preoperative diagnosis of pericardial constriction using cine computed tomography

AbstractObjectives. The purpose of this study was to determine the accuracy of cine computed tomography in the diagnosis of constrictive pericarditis.Background. Constrictive pericarditis is characterized by abnormalities of both cardiac structure and function. Accurate diagnosis requires detection of both a thickened pericardium and abnormal ventricular diastolic filling. At present, no one diagnostic technique has demonstrated sufficient accuracy in this setting. Cine computed tomography is a relatively new cardiac imaging mode with very high time and spatial resolution that has the potential to accurately diagnose constrictive pericarditis.Methods. Twelve consecutive patients were retrospectively identified who had catheterization findings suggestive of constrictive physiology, had undergone a cine computed tomographic examination and had pathologic data that delineated the status of the pericardium. Group 1 (with constrictive pericarditis; n = 5) had surgical confirmation of thickened pericardium and improved clinically after pericardiectomy. Group 2 (no constrictive pericarditis; n = 7) had cardiomyopathy with normal pericardium. Seven normal volunteers (Group 3) were also studied. Cine computed tomograms were obtained for the entire heart (8-mm slices, 17 frames/s, nonionic contrast medium). Pericardial thickness was measured at 10 ° intervals at three ventricular levels in each subject. The rapidity of diastolic filling was assessed by calculating the percent filling fraction in early diastole.Results. Pericardial thickness was 10 ± 2 mm (mean ± SD) in Group 1, 2 ± 1 mm in Group 2 and 1 ± 1 mm in Group 3 (p < 0.05, constrictive pericarditis vs. no constrictive pericarditis). Left ventricular filling fraction was 83 ± 6% in Group 1, 62 ± 9% in Group 2 and 44 ± 5% in Group 3. Right ventricular filling fraction was 93 ± 5% in Group 1, 62 ± 14% in Group 2 and 35 ± 6% in Group 3 (p < 0.05, Group 1 vs. Groups 2 and 3). Both indexes provided a clear-cut distinction between patients with and without constriction.Conclusions. Cine computed tomography simultaneously provides both anatomic and physiologic data that allow accurate preoperative diagnosis of pericardial constriction

Bedrock Geology of Scott County, Iowa

https://ir.uiowa.edu/igs_ofm/1081/thumbnail.jp

Surficial Geology of the Highlandville (Iowa) 7.5\u27\u27 Quadrangle,

https://ir.uiowa.edu/igs_ofm/1050/thumbnail.jp