In the first part of this research, we developed a differential scanning calorimetry method for calculating the initial crystallinity, change of crystallinity and crystallinity percentage of amorphous metal alloys as a function of temperature. Using thermodynamic enthalpies of amorphous, crystalline and partially devitrified specimens, our methodology can determine crystallinity percentages as low as a few percent. This technique also eliminates the need for expensive in situ accessories, such as those required in electron microscopy. In the second part, we report the effect of crystallinity percentage on the compressive deformation response of partially devitrified in situ Fe-based bulk metallic glass matrix composites (SAM25-Dev), consisting of an amorphous matrix and evenly dispersed nanocrystals (BCC iron, carbides, and borides) of sizes smaller than 20 nm. The SAM25-Dev specimens were obtained by consolidating SAM25 powders using the spark plasma sintering technique. The crystallinity percentage of the sintered samples varied between 20% and 61% depending on the sintering temperature. Macroscopically, bulk samples tested under compression exhibited an ~8% elastic deformation, which is significantly higher than elastic strains of other Fe-based bulk metallic glass composites, and strengths of ~2 GPa at fracture. Indentation toughness of the samples was below 1.6 MPa•m0.5, which categorizes the material as a brittle composite. Compression tests on micro-pillars resulted in specimen failure from the propagation of one principle shear band. Here, yield strength was corrected for the effect of taper angle of the micro-pillars and values above 5 GPa were obtained, making the material an ultra-hard composite. Such a high strength is attributed to the extremely small Poisson’s ratio (< 0.1) and higher glass transition temperature (883 K) of this material Both the compressive strength and fracture toughness of the specimens were negligibly dependent on the crystallinity percentage, implying that the radii of the plastic zones at the crack tips are smaller than the distance between nanocrystals on the specimens. Moreover, we find that SAM25-Dev shows a very high sample size dependency of strength (above 200%), which indicates a significant defect sensitivity. As a result, the residual porosity despite being minimal, strongly deteriorates the strength of the materials.

This dissertation includes exploring two scientific challenges, where both water oxidation catalysis and NH addition to alkynes will benefit greatly from the rational design of ligands. Chapter 1: The long-term goal for scientists is to use sunlight for the energy to split water. The main target of our research is the oxidation half reaction. Water oxidation catalysts have been reported by groups of Sun and Llobet but sustainable catalysis is still impaired by catalyst deactivation. This dissertation attempts to design robust catalysts through manipulating of the apical coordination sites. Chapter 2 uses phosphorus in the primary coordination sphere to create stronger axial ligand-ruthenium bonds; Chapter 3 uses a chelating macrocyclic ligand to reduce the chance of ligand loss. Chapter 4, focuses on the hydroamination of C-C multiple bonds as the most atom-efficient method for the introducing of nitrogen atoms into organic molecules.

Although most trainees in dermatology learn that different suturing techniques are designated for a specific purpose (i.e., certain functional and cosmetic outcomes), students often have a difficult time visualizing how a given suture functions in its designated capacity. In this article, we address the logic behind the most common suturing techniques in dermatologic surgery, including the direction and magnitude of their pulling force with respect to the wound edges and the ensuing displacement of dermal and epidermal structures. To aid better understanding, we diagram the vectors of suture force with each of the techniques discussed.