Engineering topics

Alvin G Yew

Publications and source records attributed to Alvin G Yew.

3 records

NASA NTRS2015

Effects of Angular Frequency During Clinorotation on Mesenchymal Stem Cell Morphology and Migration

Background/Objectives: Ground-based microgravity simulation can reproduce the apparent effects of weightlessness in spaceflight using clinostats that continuously reorient the gravity vector on a specimen, creating a time-averaged nullification of gravity. In this work, we investigated the effects of clinorotation speed on the morphology, cytoarchitecture, and migration behavior of human mesenchymal stem cells (hMSCs). Methods: We compared cell responses at clinorotation speeds of 0, 30, 60, and 75 rpm over 8 hours in a recently developed lab-on-chip-based clinostat system. Time lapse light microscopy was used to visualize changes in cell morphology during and after cessation of clinorotation. Cytoarchitecture was assessed by actin and vinculin staining, and chemotaxis was examined using time lapse light microscopy of cells in NGF (100 ng/ml) gradients. Results: Among clinorotated groups, cell area distributions indicated a greater inhibition of cell spreading with higher angular frequency (p is less than 0.005), though average cell area at 30 rpm after 8 hours became statistically similar to control (p = 0.794). Cells at 75rpm clinorotation remained viable and were able to re-spread after clinorotation. In chemotaxis chambers clinorotation did not alter migration patterns in elongated cells, but most clinorotated cells exhibited cell retraction, which strongly compromised motility.

microgravity↗

NASA NTRSDate not supplied

Enriching Heavy Noble Gases in Titan Atmosphere by Cryogenic Condensation

Titan is an extraordinary moon belonging to Saturn. It presents a dense atmosphere with a surface pressure approximately 1.45 times that of Earth’s. The relative abundance of noble gases and their isotopes can elucidate extant geochemical processes and inform past and future planetary evolution. The GCMS on the Hyugens probe sampled the dense atmosphere of Saturn’s Titan in 2005 and did not detect Kr or Xe at ppb concentrations. Several chemical pathways have been considered as mechanisms to account for the depletion of these heavy nobles. However, our understanding remains incomplete without in situ detection. Thus, we investigate spaceflight cryogenic enrichment for Kr and Xe. The thermodynamic processes would be capable of substantially amplifying these gases at femtomole concentrations, in anticipation of future atmospheric surveys on Titan.

condensation↗

NASA NTRSDate not supplied

Reducing Landing Site Contamination Using 3-D Trajectory Optimization for Surface Hoppers

Rocket-powered vehicles utilizing Vertical Take-off Vertical Landing (VTVL) are a compelling alternative to surface rovers for exploring planetary and lunar bodies. These so called “hoppers” provide enhanced mobility for accessing locations difficult to reach, and over a wider region of the surface. However, contamination and plume interactions from rocket exhaust deposited at landing sites is anticipated since landing approaches are typically along a vertical direction during the final descent. Consequently, exhaust products may alter the surface chemistry, potentially confounding compositional analysis for samples collected in the vicinity of the landing site or jeopardize mining efforts. There has been no rigorous study on flight maneuvers that can mitigate plume-to-surface interactions. A multi-objective optimization tool has been developed to simulate propulsive hops on a planetary body and minimize both fuel consumption and site alterations. Trajectories are derived by multi-objective optimization and include solutions with significant reduction in contamination for a modest increase in fuel consumption. For these solutions, surface-to-surface propulsive transfer is demonstrated, but the method can also be modified for orbit-to-surface transfers (e.g., landers).

guidance↗