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Volatiles in Protoplanetary Disks
Get PDFPlanets are assembled from the gas, dust, and ice in the accretion disks that encircle young stars. Ices of chemical compounds with low condensation temperatures (<200 K), the so-called volatiles, dominate the solid mass reservoir from which planetesimals are formed and are thus available to build the protoplanetary cores of gas/ice giant planets. It has long been thought that the regions near the condensation fronts of volatiles are preferential birth sites of planets. Moreover, the main volatiles in disks are also the main C-and O-containing species in (exo)planetary atmospheres. Understanding the distribution of volatiles in disks and their role in planet-formation processes is therefore of great interest.
This thesis addresses two fundamental questions concerning the nature of volatiles in planet-forming disks: (1) how are volatiles distributed throughout a disk, and (2) how can we use volatiles to probe planet-forming processes in disks? We tackle the first question in two complementary ways. We have developed a novel super-resolution method to constrain the radial distribution of volatiles throughout a disk by combining multi-wavelength spectra. Thanks to the ordered velocity and temperature profiles in disks, we find that detailed constraints can be derived even with spatially and spectrally unresolved data -- provided a wide range of energy levels are sampled. We also employ high-spatial resolution interferometric images at (sub)mm frequencies using the Atacama Large Millimeter Array (ALMA) to directly measure the radial distribution of volatiles.
For the second question, we combine volatile gas emission measurements with those of the dust continuum emission or extinction to understand dust growth mechanisms in disks and disk instabilities at planet-forming distances from the central star. Our observations and models support the idea that the water vapor can be concentrated in regions near its condensation front at certain evolutionary stages in the lifetime of protoplanetary disks, and that fast pebble growth is likely to occur near the condensation fronts of various volatile species. </p
Structural Characterization of Pro-inflammatory and Anti-inflammatory Immunoglobulin G Fc Proteins
Get PDFImmunoglobulin G (IgG) is central in mediating host defense due to its ability to target and eliminate invading pathogens. The fragment antigen binding (Fab) regions are responsible for antigen recognition; however the effector responses are encoded on the Fc region of IgG. IgG Fc displays considerable glycan heterogeneity, accounting for its complex effector functions of inflammation, modulation and immune suppression. Intravenous immunoglobulin G (IVIG) is pooled serum IgG from multiple donors and is used to treat individuals with autoimmune and inflammatory disorders such as rheumatoid arthritis and Kawasaki’s disease, respectively. It contains all the subtypes of IgG (IgG1-4) and over 120 glycovariants due to variation of an Asparagine 297-linked glycan on the Fc. The species identified as the activating component of IVIG is sialylated IgG Fc. Comparisons of wild type Fc and sialylated Fc X-ray crystal structures suggests that sialylation causes an increase in conformational flexibility, which may be important for its anti-inflammatory properties.
Although glycan modifications can promote the anti-inflammatory properties of the Fc, there are amino acid substitutions that cause Fcs to initiate an enhanced immune response. Mutations in the Fc can cause up to a 100-fold increase in binding affinity to activating Fc gamma receptors located on immune cells, and have been shown to enhance antibody dependent cell-mediated cytotoxicity. This is important in developing therapeutic antibodies against cancer and infectious diseases. Structural studies of mutant Fcs in complex with activating receptors gave insight into new protein-protein interactions that lead to an enhanced binding affinity.
Together these studies show how dynamic and diverse the Fc region is and how both protein and carbohydrate modifications can alter structure, leading to IgG Fc’s switch from a pro-inflammatory to an anti-inflammatory protein.</p
Palladium-Catalyzed Decarboxylative and Decarbonylative Transformations in the Synthesis of Fine and Commodity Chemicals
Get PDFDecarboxylation and decarbonylation are important reactions in synthetic organic chemistry, transforming readily available carboxylic acids and their derivatives into various products through loss of carbon dioxide or carbon monoxide. In the past few decades, palladium-catalyzed decarboxylative and decarbonylative reactions experienced tremendous growth due to the excellent catalytic activity of palladium. Development of new reactions in this category for fine and commodity chemical synthesis continues to draw attention from the chemistry community.
The Stoltz laboratory has established a palladium-catalyzed enantioselective decarboxylative allylic alkylation of β-keto esters for the synthesis of α-quaternary ketones since 2005. Recently, we extended this chemistry to lactams due to the ubiquity and importance of nitrogen-containing heterocycles. A wide variety of α-quaternary and tetrasubstituted α-tertiary lactams were obtained in excellent yields and exceptional enantioselectivities using our palladium-catalyzed decarboxylative allylic alkylation chemistry. Enantioenriched α-quaternary carbonyl compounds are versatile building blocks that can be further elaborated to intercept synthetic intermediates en route to many classical natural products. Thus our chemistry enables catalytic asymmetric formal synthesis of these complex molecules.
In addition to fine chemicals, we became interested in commodity chemical synthesis using renewable feedstocks. In collaboration with the Grubbs group, we developed a palladium-catalyzed decarbonylative dehydration reaction that converts abundant and inexpensive fatty acids into value-added linear alpha olefins. The chemistry proceeds under relatively mild conditions, requires very low catalyst loading, tolerates a variety of functional groups, and is easily performed on a large scale. An additional advantage of this chemistry is that it provides access to expensive odd-numbered alpha olefins.
Finally, combining features of both projects, we applied a small-scale decarbonylative dehydration reaction to the synthesis of α-vinyl carbonyl compounds. Direct α-vinylation is challenging, and asymmetric vinylations are rare. Taking advantage of our decarbonylative dehydration chemistry, we were able to transform enantioenriched δ-oxocarboxylic acids into quaternary α-vinyl carbonyl compounds in good yields with complete retention of stereochemistry. Our explorations culminated in the catalytic enantioselective total synthesis of (–)-aspewentin B, a terpenoid natural product featuring a quaternary α-vinyl ketone. Both decarboxylative and decarbonylative chemistries found application in the late stage of the total synthesis.</p
Quantum Mechanics Studies of Fuel Cell Catalysts and Proton Conducting Ceramics with Validation by Experiment
Get PDFWe carried out quantum mechanics (QM) studies aimed at improving the performance of hydrogen fuel cells. This led to predictions of improved materials, some of which were subsequently validated with experiments by our collaborators.
In part I, the challenge was to find a replacement for the Pt cathode that would lead to improved performance for the Oxygen Reduction Reaction (ORR) while remaining stable under operational conditions and decreasing cost. Our design strategy was to find an alloy with composition Pt3M that would lead to surface segregation such that the top layer would be pure Pt, with the second and subsequent layers richer in M. Under operating conditions we expect the surface to have significant O and/or OH chemisorbed on the surface, and hence we searched for M that would remain segregated under these conditions. Using QM we examined surface segregation for 28 Pt3M alloys, where M is a transition metal. We found that only Pt3Os and Pt3Ir showed significant surface segregation when O and OH are chemisorbed on the catalyst surfaces. This result indicates that Pt3Os and Pt3Ir favor formation of a Pt-skin surface layer structure that would resist the acidic electrolyte corrosion during fuel cell operation environments. We chose to focus on Os because the phase diagram for Pt-Ir indicated that Pt-Ir could not form a homogeneous alloy at lower temperature. To determine the performance for ORR, we used QM to examine all intermediates, reaction pathways, and reaction barriers involved in the processes for which protons from the anode reactions react with O2 to form H2O. These QM calculations used our Poisson-Boltzmann implicit solvation model include the effects of the solvent (water with dielectric constant 78 with pH 7 at 298K). We found that the rate determination step (RDS) was the Oad hydration reaction (Oad + H2Oad -> OHad + OHad) in both cases, but that the barrier for pure Pt of 0.50 eV is reduced to 0.48 eV for Pt3Os, which at 80 degrees C would increase the rate by 218%. We collaborated with the Pu-Wei Wu’s group to carry out experiments, where we found that the dealloying process-treated Pt2Os catalyst showed two-fold higher activity at 25 degrees C than pure Pt and that the alloy had 272% improved stability, validating our theoretical predictions.
We also carried out similar QM studies followed by experimental validation for the Os/Pt core-shell catalyst fabricated by the underpotential deposition (UPD) method. The QM results indicated that the RDS for ORR is a compromise between the OOH formation step (0.37 eV for Pt, 0.23 eV for Pt2ML/Os core-shell) and H2O formation steps (0.32 eV for Pt, 0.22 eV for Pt2ML/Os core-shell). We found that Pt2ML/Os has the highest activity (compared to pure Pt and to the Pt3Os alloy) because the 0.37 eV barrier decreases to 0.23 eV. To understand what aspects of the core shell structure lead to this improved performance, we considered the effect on ORR of compressing the alloy slab to the dimensions of pure Pt. However this had little effect, with the same RDS barrier 0.37 eV. This shows that the ligand effect (the electronic structure modification resulting from the Os substrate) plays a more important role than the strain effect, and is responsible for the improved activity of the core- shell catalyst. Experimental materials characterization proves the core-shell feature of our catalyst. The electrochemical experiment for Pt2ML/Os/C showed 3.5 to 5 times better ORR activity at 0.9V (vs. NHE) in 0.1M HClO4 solution at 25 degrees C as compared to those of commercially available Pt/C. The excellent correlation between experimental half potential and the OH binding energies and RDS barriers validate the feasibility of predicting catalyst activity using QM calculation and a simple Langmuir–Hinshelwood model.
In part II, we used QM calculations to study methane stream reforming on a Ni-alloy catalyst surfaces for solid oxide fuel cell (SOFC) application. SOFC has wide fuel adaptability but the coking and sulfur poisoning will reduce its stability. Experimental results suggested that the Ni4Fe alloy improves both its activity and stability compared to pure Ni. To understand the atomistic origin of this, we carried out QM calculations on surface segregation and found that the most stable configuration for Ni4Fe has a Fe atom distribution of (0%, 50%, 25%, 25%, 0%) starting at the bottom layer. We calculated that the binding of C atoms on the Ni4Fe surface is 142.9 Kcal/mol, which is about 10 Kcal/mol weaker compared to the pure Ni surface. This weaker C binding energy is expected to make coke formation less favorable, explaining why Ni4Fe has better coking resistance. This result confirms the experimental observation. The reaction energy barriers for CHx decomposition and C binding on various alloy surface, Ni4X (X=Fe, Co, Mn, and Mo), showed Ni4Fe, Ni4Co, and Fe4Mn all have better coking resistance than pure Ni, but that only Ni4Fe and Fe4Mn have (slightly) improved activity compared to pure Ni.
In part III, we used QM to examine the proton transport in doped perovskite-ceramics. Here we used a 2x2x2 supercell of perovskite with composition Ba8X7M1(OH)1O23 where X=Ce or Zr and M=Y, Gd, or Dy. Thus in each case a 4+ X is replace by a 3+ M plus a proton on one O. Here we predicted the barriers for proton diffusion allowing both includes intra-octahedron and inter-octahedra proton transfer. Without any restriction, we only observed the inter-octahedra proton transfer with similar energy barrier as previous computational work but 0.2 eV higher than experimental result for Y doped zirconate. For one restriction in our calculations is that the Odonor-Oacceptor atoms were kept at fixed distances, we found that the barrier difference between cerates/zirconates with various dopants are only 0.02~0.03 eV. To fully address performance one would need to examine proton transfer at grain boundaries, which will require larger scale ReaxFF reactive dynamics for systems with millions of atoms. The QM calculations used here will be used to train the ReaxFF force field.</p
Biological Activity of Rhodium Metalloinsertors and the Design of Bifunctional Conjugates
Get PDFThe Barton laboratory has established that octahedral rhodium complexes bearing the sterically expansive 5,6-chrysene diimine ligand can target thermodynamically destabilized sites, such as base pair mismatches, in DNA with high affinity and selectivity. These complexes approach DNA from the minor groove, ejecting the mismatched base pairs from the duplex in a binding mode termed metalloinsertion. In recent years, we have shown that these metalloinsertor complexes also exhibit cytotoxicity preferentially in cancer cells that are deficient in the mismatch repair (MMR) machinery.
Here, we establish that a sensitive structure-activity relationship exists for rhodium metalloinsertors. We studied the relationship between the chemical structures of metalloinsertors and their effect on biological activity for ten complexes with similar DNA binding affinities, but wide variation in their lipophilicity. Drastic differences were observed in the selectivities of the complexes for MMR-deficient cells. Compounds with hydrophilic ligands were highly selective, exhibiting preferential cytotoxicity in MMR-deficient cells at low concentrations and short incubation periods, whereas complexes with lipophilic ligands displayed poor cell-selectivity. It was discovered that all of the complexes localized to the nucleus in concentrations sufficient for mismatch binding; however, highly lipophilic complexes also exhibited high mitochondrial uptake. Significantly, these results support the notion that mitochondrial DNA is not the desired target for our metalloinsertor complexes; instead, selectivity stems from targeting mismatches in genomic DNA.
We have also explored the potential for metalloinsertors to be developed into more complex structures with multiple functionalities that could either enhance their overall potency or impart mismatch selectivity onto other therapeutic cargo. We have constructed a family of bifunctional metalloinsertor conjugates incorporating cis-platinum, each unique in its chemical structure, DNA binding interactions, and biological activity. The study of these complexes in MMR-deficient cells has established that the cell-selective biological activity of rhodium metalloinsertors proceeds through a critical cellular pathway leading to necrosis.
We further explored the underlying mechanisms surrounding the biological response to mismatch recognition by metalloinsertors in the genome. Immunofluorescence assays of MMR-deficient and MMR-proficient cells revealed that a critical biomarker for DNA damage, phosphorylation of histone H2AX (γH2AX) rapidly accumulates in response to metalloinsertor treatment, signifying the induction of double strand breaks in the genome. Significantly, we have discovered that our metalloinsertor complexes selectively inhibit transcription in MMR-deficient cells, which may be a crucial checkpoint in the eventual breakdown of the cell via necrosis. Additionally, preliminary in vivo studies have revealed the capability of these compounds to traverse the complex environments of multicellular organisms and accumulate in MMR-deficient tumors. Our ever-increasing understanding of metalloinsertors, as well as the development of new generations of complexes both monofunctional and bifunctional, enables their continued progress into the clinic as promising new chemotherapeutic agents. </p
Everybody Farts: Celebrating the Body and Refuting Medical Paternalism in Joyce's Ulysses
Get PDFJames Joyce’s Ulysses celebrates all facets of daily life in its refusal to censor raw human emotions and emissions. He adopts a critically medical perspective to portray this honest, unfiltered narrative. In doing so, he reveals the ineffectiveness of the physician-patient relationship due to doctors’ paternalistic attitudes that hinder nonjudgmental, open listening of this unfiltered narrative. His exploration of the doctor’s moral scrutiny, cultural prejudices, and authoritative estrangement from the patient underscore the importance in remembering that physicians and patients alike are ultimately just fellow human beings. Wryly, he drives this point to literal nausea, as his narrative proudly asserts the revulsive details of public health, digestion, and death. In his gritty ruminations on the human body’s material reality, Joyce mocks the physician’s highbrow paternalism by forcing him to identify with the farting, vomiting, decaying bodies around him. In celebrating the uncensored human narrative, Joyce challenges physician and patient alike to openly listen to the stories of others
Applications of Nuclear Resonant Scattering to Further Our Understanding of Earth’s Interior
Get PDFThe elastic and the thermodynamic properties of minerals under extreme P-T conditions are of general importance to the geodynamic modeling and the interpretation of seismic-wave observations. An accurate laboratory determination of these properties provides constraints to determine the composition and temperature of Earth's interior. In this thesis, I focus on the application of nuclear resonant scattering, an advanced synchrotron based spectroscopic technique, to further our understanding of candidate materials in Earth's interior. Specific examples include enstatite, which is an abundant mineral in the mantle, and iron-nickel alloy, which is believed to be the major component of the core. Our nuclear resonant scattering experiments is complemented with other synchrotron based techniques, such as diffraction.
Nuclear resonant scattering is capable of detecting subtle changes in the mineral's hyperfine parameters, and can therefore be sensitive to the transitions occurring in minerals under pressure. For example, we explore the site-specific hyperfine behavior of iron in a 57Fe-enriched powdered enstatite sample using nuclear resonant scattering and diamond-anvil cells in two independent experiments. The (Mg0.980Fe0.020(5) )(Mg0.760Fe0.240)Si2O6 sample is pressurized up to 36 GPa at ambient temperature. In one experiment, NaCl is used as the pressure-transmitting medium, and in the other experiment, Ne surround the sample. Analyses of both data sets reveal a change in the trend or discontinuity in the hyperfine parameters around 10 GPa, indicative of a structural transformation in enstatite. However, the detailed behaviors of the iron sites with pressure appear to depend on the local stress conditions provided by the different pressure media.
Nuclear resonant scattering is also used to measure the elastic properties of iron-bearing enstatite at high pressures. The behavior of synthetic powdered 57Fe-enriched (Mg0.980Fe0.020(5) )(Mg0.760Fe0.240)Si2O6 is explored by X-ray diffraction (XRD) and nuclear resonance inelastic X-ray scattering (NRIXS). The Pbca-structured enstatite sample is compressed in fine pressure increments for our XRD measurements. One structural transition between 10.1 and 12.2 GPa is identified from the XRD data. The XRD reflections observed for the high-pressure phase are best matched with space group P21/c. The partial phonon density of states (DOS) is derived from the raw NRIXS data up to 17 GPa, and from the low-energy region of the DOS, the Debye sound velocity is determined. We use the equation of state determined from XRD and Debye sound velocity to compute the isotropic compressional and shear wave velocities of enstatite at different pressures. We combine density-functional theory with nuclear resonant scattering to understand the local site symmetry of the Fe atoms in our sample. We compare our experimental results with seismic observations to understand large lateral variations in shear wave velocities in the upper mantle.
Recently, nuclear resonant scattering has been shown to be a powerful probe in determining the solid-liquid boundary of iron-bearing materials. To capture the sample's transient temperature fluctuations and reduce uncertainties in melting temperatures, we have developed a Fast Temperature Readout (FasTeR) spectrometer in-line with nuclear resonant scattering measurements under extreme conditions at Sector 3-ID-B of the Advanced Photon Source at Argonne National Laboratory. Dedicated to determining the sample's temperature near its melting point, FasTeR features a fast readout rate (about 100 Hz), high sensitivity, large dynamic range and well-constrained focus. FasTeR is capable of reading out temperatures about 1 to 2 magnitudes faster than the conventional CCD spectrometer, without sacrificing accuracy, and is especially suitable for dynamic measurements at extreme conditions.
By combining nuclear resonant scattering with the laser heated diamond anvil cell and the FasTeR spectrometer, we have determined the melting temperatures of fcc-structured iron and iron-nickel alloy at high pressures. We find that the melting curve of Fe is slightly higher than the melting curve of Fe0.9Ni0.1, but the difference is smaller than the uncertainty. We calculate the fcc-hcp-l triple point of Fe0.9Ni0.1 to be 117±3 GPa and 3285±200 K, and 111±3 GPa and 3390±200 K for Fe. With the fcc-hcp-l triple points of Fe and Fe0.9Ni0.1, and the thermophysical parameters of hcp-Fe determined from a NRIXS measurement, we compute the high pressure melting curves of hcp-structured Fe and Fe0.9Ni0.1. We estimate the upper bound of Earth's inner core-outer core boundary temperature as ~5600±200 K, and we compute the upper bound of outer core temperature with an adiabatic model. We discuss the implications of these temperatures on the phase relations of deep Earth materials.</p
Shakespeare’s Crafting of the Ideal King in Henry V
No full text[Introduction] In Shakespeare’s history Henry V, the playwright depicts the reign of King Harry—
specifically with respect to his claim to the throne of France and his subsequent invasion. In the
prequel to this play, Henry IV, Harry is shown as an impetuous young boy who engages in
mischief around town with his immature friends. However, by the end of the first part of Henry
IV, Harry matures and becomes a brave, strong warrior on the battlefield as well as a courageous,
honorable man. He is ultimately portrayed as the rightful heir to the throne. At the beginning of
Henry V, the audience sees a mature king who has been in charge of the kingdom for some time
already. While Shakespeare bases his plays on historical events as documented in works like
Raphael Holinshed’s Chronicles of England, Scotland, and Ireland, the playwright uses his
literary liberty to alter the chronological order of events and even sometimes the actions that
certain characters take or do not take. Shakespeare’s dramatization of several historical elements
of Holinshed serves to aggrandize the glory and maturity of Henry V as a just, idealized king;
with his decisions to change what is written in the history books, Shakespeare highlights the king’s military aptitude, his modesty in dealing with his soldiers and citizens, and his political
savviness
Discovery of Active Cis-Regulatory Elements and Transcription Factor Footprints in Nematodes Using Functional Genomics Approaches
Get PDFHigh throughput DNA sequencing has emerged as a versatile and inexpensive readout of functional activity in biological organisms. In this study I describe the implementation of DNaseI hypersensitivity assays using deep sequencing (DNase-seq) to systematically identify Caenorhabditis elegans cis-regulatory modules (CRMs) in embryonic and L1 arrest larval life stages in an unbiased and de novo manner. We validated our data by comparison to many known enhancers of lin-39/ceh-13 Hox complex and of hlh-1, myo-2, myo-3, lin-26, and other important developmental genes and are also able to predict novel cis-regulatory modules. We predict novel regulatory motifs from our DNase-seq data and predict potential regulatory functions using gene ontology and anatomy enrichment analysis. In addition, our data are high-resolution enough to identify binding sites of transcription factors in the genome. Our data provide support for many distal CRMs in C. elegans and for a significant portion of genes possessing multiple CRMs. DNase-seq data can also be used to refine prediction of tissue-specific genes such as those regulated by C. elegans pan-neuronal N1 and intestinal ELT-2 DNA motifs. Overall, we identify 24,128 putative CRMS containing over 55,000 footprints. In L1 arrest, we identify 15,841 putative CRMs in the L1 arrest larvae containing 32,000 TF footprints. From comparison of these datasets, we identify an additional 1,854 noncoding DHS that appear to be specific to the L1 arrest larvae condition. These genes include downstream targets of signaling pathways known to be regulated during L1 arrest such as insulin-like signaling via DAF-16/FOXO and Forkhead box transcription factor PHA-4/FOXA that impacts starvation survival in the L1 arrest condition. Having established the first proof-of-principle DNase-seq in nematodes using C. elegans, I am applying DNase-seq to a distantly related entomopathogenic nematode, Steinernema carpocapsae, with a recently sequenced genome and transcriptome. Finally, I am using a massively parallel reporter assay to test the functional activity of the CRMs we have discovered from DNase-seq using two reporter designs based on MPRA and STARR-seq and by performing DNA and RNA sequencing on transgenic C. elegans.</p
Shock Wave Behavior of Particulate Composites
Get PDFMaterial heterogeneity at some scale is common in present engineering and structural materials as a means of strength improvement, weight reduction, and performance enhancement in a great many applications such as impact and blast protection, construction, and aerospace. While the benefits of transitioning toward composites in practical applications is obvious, the methods of measurement and optimization required to handle spatial heterogeneity and bridge length scale differences across multiple orders of magnitude are not. This is especially true as loading rates transition into the shock regime. Composite materials, such as concrete, have advantages afforded to them by their microstructure that allow them to dissipate and scatter impact energy. The mechanical mismatch between constituent phases in composites (mortar and cement paste in concrete, crystals and binder in polymer bonded explosives, ceramic powder and epoxy in potting materials, etc.) provides the interfaces required for shock wave reflection. The degree to which a shock is disrupted from its accepted form as a propagating discontinuity in stress and particle velocity is highly dependent upon the size, shape, and density of the interfaces present.
The experimental and computer aided simulations in this thesis seek to establish a scaling relationship between composite microstructure and shock front disruption in terms of particulate size and density through the use of multi-point heterodyne velocity interferometry. A model particulate composite has been developed to mimic the wave reflection properties of materials such as Ultra High Performace Composite (UHPC) concrete and polymer bonded explosives, while also being simple to source and manufacture repeatably. Polymethyl Methacrylate (PMMA), a thermoplastic polymer, and silica glass spheres satisfy the manufacturing constraints with a shock impedance mismatch of 4.1, when placed in-between the shock impedance of UHPC concretes (~ 10) and polymer bondedexplosives (~ 2). The flexibility afforded by the model composite allows for the use of mono-disperse bead particle diameter distributions centered at 5 discrete diameters centered in the range associated with high scattering effectiveness (5-50 times the shock thickness in the pure matrix material). Shock front disruption is measured at multiple points on the rear surface of a plate impact target to observe shock spreading and spatial heterogeneity in material response due to random particle placement.
Shock rise times are reported for composites of 30% and 40% glass spheres by volume, with glass spheres of 100, 300, 500, 700, and 1000 micron diameter. Composites with single mode as well as bi-modal bead diameter distributions are subjected to plate impact loading at an average pressure of 5 GPa. In single mode composites, a linear dependence of shock wave rise time on particle diameter is observed, with a constant of proportionality equal to the bulk shock speed in the material. Bi-modal bead diameter composites were fabricated in order to achieve higher volume fractions without composite degradation. The addition of a second phase to a base 30% glass by volume composite mix results in significant increases in shock wave rise time for base mixes of 500 micron beads, while a point of maximum scattering effectiveness is observed for base mixes
of 1000 micron diameter beads.
A comprehensive two dimensional series of CTH hydrocode simulations has been completed in tandem with experiments. An evaluation of the discrepancies in simulation and experimental results is presented. Shock disruption mechanisms and matrix/interface damage effects are discussed as possible sources of error and potential avenues for model improvement. The scaling arguments and model deficiency corrections made in this thesis have the potential to drive the development of new approaches of modeling shock waves in heterogeneous materials as well as optimization of microstructure for maximum shock front disruption.</p