Realistic Air Filter Media Performance Simulation. Part I: Navier-Stokes / Finite-Volume CFD Procedures

A review of published studies of numerical techniques for air filter performance simulation shows that there are two general approaches to such simulations. One describes gases flowing through filter media as continuous fluids, influenced by themacro properties viscosity, density, and pressure. The alternate approach treats gases as molecules in random motion, impacting their own kind and solid surfaces on a micro-scale. The appropriate form for a given filter medium and operating condition depends on the gas properties and the Knudsen number (Kn) of the smallest fibers in the filter medium simulated. When no fiber Kn exceeds 0.01, the Navier-Stokes equation and finite-volume solutions should simulate filter media pressure drop and particle capture reliably, if correct particle and fiber boundary conditions, including "slip" at boundaries, are employed. In addition, fibrous media geometry must be modeled in enough detail to make simulation results match experimental data. Part I of this study reviews literature related to filter media flow and particle-capture simulation in the continuum regime using the finite-volume method for flow calculations; appropriate boundary conditions and parameter values are suggested. Part II discusses media simulation in flow regimes where other equations and computation techniques must be use

Laser Ranging Interferometry for Future Gravity Missions : Instrument Design, Link Acquisition and Data Calibration

The presented study aims to improve the design solution adopted for the Laser Ranging Instrument of the GRACE Follow-On mission in terms of instrument layout, algorithms for the laser link acquisition and techniques for mitigating the range measurement noise. The first part of this work describes viable layout solutions of a heterodyne interferometer employed for intra-satellite range metrology and the major noise contributions which degrade the overall accuracy of the instrument. Together with the optical layout of the instrument, novel design concepts of the instrumenta s subsystems are also analyzed and tested. Precisely, a phasemeter designed to autonomously acquire and track a heterodyne signal with low signal-to-noise ratio in a frequency band that spans from 1MHz to 25MHz is presented. Particular attention is also dedicated to the mathematical modeling of the steering mirror dynamics and to the enhancement of its pointing performance by means of feedforward control. In the second part of this work, solutions for autonomously acquiring a laser signal buried in noise are analyzed and put in relation with the boundary constraints of the acquisition problem. The acquisition algorithms presented and the robustness of their design is verified mainly using numerical simulations. Experimental tests have also been performed for validating the simulation hypothesis and verifying their compliancy to a realistic mission scenario. The last part of this work describes a calibration algorithm which has been developed for minimizing, during data post-processing, the noise due to the tilt-to-piston coupling which represents one of the highest contributors to the overall measurement noise

Supernova / Acceleration Probe: A Satellite Experiment to Study the Nature of the Dark Energy

The Supernova / Acceleration Probe (SNAP) is a proposed space-based experiment designed to study the dark energy and alternative explanations of the acceleration of the Universe's expansion by performing a series of complementary systematics-controlled measurements. We describe a self-consistent reference mission design for building a Type Ia supernova Hubble diagram and for performing a wide-area weak gravitational lensing study. A 2-m wide-field telescope feeds a focal plane consisting of a 0.7 square-degree imager tiled with equal areas of optical CCDs and near infrared sensors, and a high-efficiency low-resolution integral field spectrograph. The SNAP mission will obtain high-signal-to-noise calibrated light-curves and spectra for several thousand supernovae at redshifts between z=0.1 and 1.7. A wide-field survey covering one thousand square degrees resolves ~100 galaxies per square arcminute. If we assume we live in a cosmological-constant-dominated Universe, the matter density, dark energy density, and flatness of space can all be measured with SNAP supernova and weak-lensing measurements to a systematics-limited accuracy of 1%. For a flat universe, the density-to-pressure ratio of dark energy can be similarly measured to 5% for the present value w0 and ~0.1 for the time variation w'. The large survey area, depth, spatial resolution, time-sampling, and nine-band optical to NIR photometry will support additional independent and/or complementary dark-energy measurement approaches as well as a broad range of auxiliary science programs. (Abridged)Comment: 40 pages, 18 figures, submitted to PASP, http://snap.lbl.go

Wide-Field InfraRed Survey Telescope (WFIRST) Final Report

In December 2010, NASA created a Science Definition Team (SDT) for WFIRST, the Wide Field Infra-Red Survey Telescope, recommended by the Astro 2010 Decadal Survey as the highest priority for a large space mission. The SDT was chartered to work with the WFIRST Project Office at GSFC and the Program Office at JPL to produce a Design Reference Mission (DRM) for WFIRST. Part of the original charge was to produce an interim design reference mission by mid-2011. That document was delivered to NASA and widely circulated within the astronomical community. In late 2011 the Astrophysics Division augmented its original charge, asking for two design reference missions. The first of these, DRM1, was to be a finalized version of the interim DRM, reducing overall mission costs where possible. The second of these, DRM2, was to identify and eliminate capabilities that overlapped with those of NASA's James Webb Space Telescope (henceforth JWST), ESA's Euclid mission, and the NSF's ground-based Large Synoptic Survey Telescope (henceforth LSST), and again to reduce overall mission cost, while staying faithful to NWNH. This report presents both DRM1 and DRM2.Comment: 102 pages, 57 figures, 17 table

Development of Nanostructures by Atomic and Molecular Layer Deposition

Atomic layer deposition (ALD) is a thin film deposition technique that has a rich history of being an enabling technique. This vapor phase deposition process can produce a variety of thin films and nanostructures. ALD is based on sequential, self-limiting reactions and provides angstrom level control over film growth. Furthermore, ALD allows for conformal deposition on high-aspect ratio structures and can provide tunable film composition. As nanotechnology marches forward, the development of nanomaterials has significantly advanced. Additional functionality can be imparted to nanomaterials by using surface modification techniques. Given the advantages of ALD, this technique has become a powerful tool for modifying the surface of materials and increasing the functionality and application of nanomaterials. The toolkit of available materials for surface modification is further augmented by including molecular layer deposition (MLD), a technique used to grow organic polymer-like materials. By combining ALD and MLD together, novel inorganic-organic hybrid materials can be produced with specifically tailored properties. The first part in the thesis investigates the effect of ozone on nitrogen doped carbon nanotubes (NCNTs) and pristine carbon nanotubes (PCNTs). The deleterious effects of ozone were found to occur only for NCNTs, while little to or no damage occurs for PCNTs. Furthermore, this work highlights the importance of understanding precursor-substrate interaction, especially when dealing with nanomaterials. The second and third part of this thesis outline the synthesis of novel thin films made by ALD and MLD. First, an aluminum alkoxide film with tunable conductivity was made using trimethylaluminium (TMA), ethylene glycol (EG), and terephthaloyl chloride in various subcycle configurations to control the ratio of aluminum to carbon in the film. The films were then pyrolyzed in a reducing atmosphere to yield a conductive aluminum oxide/carbon composite. Depending on the ratio of aluminum to carbon in the grown film, post-pyrolyzed films displayed varying levels of electronic conductivity. Synchrotron based XPS was then used to elucidate the origin of conductivity within the film. The second novel film is a mixed inorganic-organic polyurea film. For the first time, polarization-dependent x-ray absorption spectroscopy was used to determine the difference in orientation and ordering between pure organic polyurea films and inorganic-organic polyurea films. In-depth analysis of this data revealed that the hybrid inorganic-organic films possessed a high degree of ordering compared to their organic counterpart. Both studies present the possibility of combining ALD and MLD in tuning various film properties such as electronic conductivity and oligomer packing density. The fourth part of this thesis investigates the formation of single-atom and ultra-small clusters of platinum produced by ALD. The self-limiting characteristics of trimethyl(methylcyclopentadienyl)-platinum on NCNTs and PCNTs was investigated by varying precursor exposure time and determining the influence of reactor temperature. This study determined that a 1 minute exposure of the Pt precursor at 250°C yielded primarily single atoms and ultra-small clusters on NCNTs, but not PCNTs. Extended x-ray fine structure analysis was conducted to determine the bonding characteristics of Pt to NCNTs and PCNTs. This study outlines the necessary conditions to deposit single atom and ultra-small clusters of Pt on carbon nanotube substrates and the parameters that influence this process. The final experimental investigation of this thesis is the protection of metallic lithium (Li) by ALD and MLD. Fifty cycles of either TMA-H2O, TMA-EG or TMA-glycerol (GLY) were used to coat the surface of Li metal. Galvanostatic cycling of Li symmetric cells was then conducted to determine the protective capabilities of these films. The results revealed that electrodes coated with TMA-GLY provided prolonged cyclability of metallic Li electrodes. For the first-time gravimetric intermission titration technique was then conducted on coated electrodes to unravel the effects of lithium electrodissolution and electroplating. This study demonstrated that the longevity of TMA-GLY coated electrodes originates from the relatively low overpotential required to plate and strip Li from the MLD film. Finally, scanning electron microscopy and Rutherford backscattering spectometry was used to determine composition and morphology of the formed solid electrolyte interphase on coated electrodes following electrochemical cycling