A study to improve the mechanical properties of silicon carbide ribbon fibers

Preliminary deposition studies of SiC ribbon on a carbon ribbon substrate showed that the dominant strength limiting flaws were at the substrate surface. Procedures for making the carbon ribbon substrate from polyimide film were improved, providing lengths up to 450 meters (1,500 ft.) of flat carbon ribbon substrate 1,900 microns (75 mils) wide by 25 microns (1 mil) thick. The flaws on the carbon ribbon were smaller and less frequent than on carbon ribbon used earlier. SiC ribbon made using the improved substrate, including a layer of pyrolytic graphite to reduce further the severity of substrate surface flaws, showed strength levels up to the 2,068 MPa (300 Ksi) target of the program, with average strength levels over 1,700 MPa (250 Ksi) with coefficient of variation as low as 10% for some runs

New numerical approaches for modeling thermochemical convection in a compositionally stratified fluid

Seismic imaging of the mantle has revealed large and small scale heterogeneities in the lower mantle; specifically structures known as large low shear velocity provinces (LLSVP) below Africa and the South Pacific. Most interpretations propose that the heterogeneities are compositional in nature, differing in composition from the overlying mantle, an interpretation that would be consistent with chemical geodynamic models. Numerical modeling of persistent compositional interfaces presents challenges, even to state-of-the-art numerical methodology. For example, some numerical algorithms for advecting the compositional interface cannot maintain a sharp compositional boundary as the fluid migrates and distorts with time dependent fingering due to the numerical diffusion that has been added in order to maintain the upper and lower bounds on the composition variable and the stability of the advection method. In this work we present two new algorithms for maintaining a sharper computational boundary than the advection methods that are currently openly available to the computational mantle convection community; namely, a Discontinuous Galerkin method with a Bound Preserving limiter and a Volume-of-Fluid interface tracking algorithm. We compare these two new methods with two approaches commonly used for modeling the advection of two distinct, thermally driven, compositional fields in mantle convection problems; namely, an approach based on a high-order accurate finite element method advection algorithm that employs an artificial viscosity technique to maintain the upper and lower bounds on the composition variable as well as the stability of the advection algorithm and the advection of particles that carry a scalar quantity representing the location of each compositional field. All four of these algorithms are implemented in the open source FEM code ASPECT

A Qualitative Assessment of the International Exposition Center to the Greater Cleveland Area

This report describes the outcomes of discussions with IX Center customers and stakeholders as to how the IX Center qualitatively impacts the greater Cleveland area. The results suggest that while the IX Center is perceived to be an asset by customers and stakeholders, it’s likely that the IX Center will need to develop strategies to remain competitive with similar convention centers across the country

An Acoustic Technique for the Noninvasive in-Situ Measurement of Crystal Size and Solution Concentration

We demonstrated the use of acoustic measurements for tracking potassium dihydrogen phosphate (KDP) crystal growth. Both KDP solution concentration and KDP crystal size can be found by using information derived from acoustic wave propagation in the solution. Acoustic measurements show good correlation to conductivity measurements for KDP solution concentration

Bone Marrow Stromal Cells: Characterization and Clinical Application

The bone marrow stroma consists of a heterogeneous population of cells that provide the structural and physiological support for hematopoietic cells. Additionally, the bone marrow stroma contains cells with a stem-cell-like character that allows them to differentiate into bone, cartilage, adipocytes, and hematopoietic supporting tissues. Several experimental approaches have been used to characterize the development and functional nature of these cells in vivo and their differentiating potential in vitro. In vivo, presumptive osteogenic precursors have been identified by morphologic and immunohistochemical methods. In culture, the stromal cells can be separated from hematopoietic cells by their differential adhesion to tissue culture plastic and their prolonged proliferative potential. In cultures generated from single-cell suspensions of marrow, bone marrow stromal cells grow in colonies, each derived from a single precursor cell termed the colony-forming unit-fibroblast. Culture methods have been developed to expand marrow stromal cells derived from human, mouse, and other species. Under appropriate conditions, these cells are capable of forming new bone after in vivo transplantation. Various methods of cultivation and transplantation conditions have been studied and found to have substantial influence on the transplantation outcome The finding that bone marrow stromal cells can be manipulated in vitro and subsequently form bone in vivo provides a powerful new model system for studying the basic biology of bone and for generating models for therapeutic strategies aimed at regenerating skeletal elements.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68070/2/10.1177_10454411990100020401.pd

DC Link Stabilized Field Oriented Control of Electric Propulsion Systems

Induction motor based electric propulsion systems can be used in a wide variety of applications including locomotives, hybrid electric vehicles, and ships. Field oriented control of these drives is attractive since it allows the torque to be tightly and nearly instantaneously controlled. However, such systems can be prone to negative impedance instability of the DC link. This paper examines this type of instability and sets forth a readily implemented albeit nonlinear control strategy to mitigate this potential problem

Magnetohydrodynamic scaling: From astrophysics to the laboratory

During the last few years, considerable progress has been made in simulating astrophysical phenomena in laboratory experiments with high-power lasers. Astrophysical phenomena that have drawn particular interest include supernovae explosions; young supernova remnants; galactic jets; the formation of fine structures in late supernovae remnants by instabilities; and the ablation-driven evolution of molecular clouds. A question may arise as to what extent the laser experiments, which deal with targets of a spatial scale of ∼100 μm and occur at a time scale of a few nanoseconds, can reproduce phenomena occurring at spatial scales of a million or more kilometers and time scales from hours to many years. Quite remarkably, in a number of cases there exists a broad hydrodynamic similarity (sometimes called the “Euler similarity”) that allows a direct scaling of laboratory results to astrophysical phenomena. A discussion is presented of the details of the Euler similarity related to the presence of shocks and to a special case of a strong drive. Constraints stemming from the possible development of small-scale turbulence are analyzed. The case of a gas with a spatially varying polytropic index is discussed. A possibility of scaled simulations of ablation front dynamics is one more topic covered in this paper. It is shown that, with some additional constraints, a simple similarity exists. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71174/2/PHPAEN-8-5-1804-1.pd

Heterogeneous perturbations in the Doppler-free S1 ← S0 two-photon spectrum of benzene: Evidence for intrastate coupling

Rotational perturbations are identified in Doppler-free two-photon spectra of the 1410 and 1410110 vibronic bands in C6H6. Evidence is found that Coriolis coupling between some of the rotational levels of two distinct vibrational states within S1 is the mechanism responsible. This coupling mechanism is thought to be responsible for irreversible intramolecular relaxation at higher excess energies and higher vibrational state densities