Indiana University-Purdue University Indianapolis (IUPUI) / Objective: Nutritional assessment and diagnosis of malnutrition in pediatric patients is dependent on anthropometric measurements. In macrocephalic children, current anthropometric measures may fail to correctly diagnose malnutrition. The purpose of this study is to determine if the measurement of mid-upper arm circumference (MUAC) in pediatric patients with macrocephaly better identifies children at nutritional risk as compared to weight-for-length (WFL) or body mass index (BMI). Methods: A cross-sectional pilot study of children aged 6-36 months with a head circumference 2 SD above the mean was performed. Visual assessment was used as the clinical “gold standard” for presence of malnutrition. MUAC was compared to the WFL or BMI for each child to determine which anthropometric measurement better identified presence of malnutrition. Statistics: Two-way contingency tables were used to summarize the relationships between each pair of assessments of whether a child is malnourished. Agreement between the methods was evaluated using kappa statistics and percent agreement. Analyses were performed using SAS version 9.4 ™ statistical software. Results: Twenty patients were included who met study criteria. The mean head circumference z-score was 2.6. The mean BMI/WFL z-score was 0.9, which would qualify the child as “nourished.” Of the 20 children included in the study, 20% (n=4) appeared visually malnourished on physical exam. BMI/WFL confirmed diagnosis of malnutrition in 75% (n=3) of children. MUAC confirmed diagnosis of malnutrition in 75% (n=3) of children. Diagnosis of malnutrition using BMI/WFL as compared to visual assessment had a non-significant p-value of 0.317. Diagnosis of malnutrition using MUAC as compared to visual assessment had a non-significant p-value of 0.317. With a p-value of >0.5, there is no statistically significant difference between BMI/WFL and MUAC in diagnosis of malnutrition. Conclusion: MUAC did not perform better than BMI/WFL at identifying malnutrition in pediatric macrocephalic patients.

Sensing systems for mid-infrared wavelengths (2 to 5 μm) have important applications in biomedical, atmospheric and process gas monitoring systems. For lack of a suitable substrate, the full potential of GaSb-based materials, which are particularly suitable for operating in these wavelengths, are not completely realized. Hence, metamorphic growth technology, that allows the growth of semiconductor epilayers of arbitrary composition on any substrate, has been explored for antimony materials in this research. This makes the growth of device layers, containing arbitrary composition of GaSb-based materials, possible on commercially available 6"-GaAs substrates, and thereby reducing fabrication cost. Metamorphic growth of In(0.15)Ga(0.85)Sb was achieved using gas-source molecular beam epitaxy by growing compositionally graded ln(x)Ga(1-x)Sb buffer layers on a GaSb substrate. The effects of growth temperature on the quality of the metamorphic buffer layers along with the etching issues (both wet and dry) of GaSb-based materials were studied. Homo-junction n-i-p and p-i-n diodes were fabricated on In(0.15)Ga(0.85)Sb metamorphic layers. The dark current and its temperature dependence were measured and the extraction of area and perimeter components of dark current was done. The modeling of the components of dark current suggests that the diode currents were dominated by surface leakage. Surface passivation by silicon nitride and polyimide were investigated and our findings suggest that the former resulted in a better passivated surface. Responsivity measurements show that In(0.18)Ga(0.82)Sb diodes, metamorphically grown on GaSb substrates, have a cut-off wavelength of 2270 nm. Finally, hole (β) and previously unreported electron (α) ionization coefficients, at room temperature and 90° C, were extracted from these structures. The results show that α>β for ln(0.10)Ga(0.90)Sb for both temperatures. These photodetectors can be implemented m practical receiver systems for mid-infrared applications, such as atmospheric CO2 and methane detection at 2.0 μm. The possibility of growing antimony-based device layers on larger substrates, paves the way for future optoelectronic receiver systems operating at longer wavelengths, where both the photodetector and the amplifier can be integrated in the same module. / Thesis / Doctor of Philosophy (PhD)

<p> Previous workers in the Hamilton area have pointed out the occurance of lead and zinc mineralization within the Mid-Silurian carbonate beds. They also mentioned the existance of bitumens in these rock units.</p> <p> Analysis of 30 dolomite samples and separated bitumens by atomic absorption for Cu, Pb, Zn showed that the localization of the metals in the carbonates was controlled by the concentration of the bitumens in the rocks.</p> <p> Analysis of 5 bitumens samples by atomic absorption for Cu, Pb, Zn suggested that the bitumens act merely as a reducing agent and are not preferred sites for base metal accumulation.</p> / Thesis / Bachelor of Science (BSc)

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Large-scale optoelectronic integration is limited by the lack of efficient light sources and broadband photodetectors, which could be integrated with the silicon complementary metal-oxide-semiconductor (CMOS) technology. Persistent efforts continue to achieve efficient light emission as well as broadband photodetection from silicon in extending the silicon technology into fully integrated optoelectronic circuits. Recent breakthroughs, including the demonstration of high-speed optical modulators, photodetectors, and waveguides in silicon, have brought the concept of transition from electrical to optical interconnects closer to realization. The on-chip light sources based on silicon are still a key challenge due to the indirect bandgap of silicon that impedes coherent light sources. To overcome this issue, we have studied, fabricated, and characterized nanostructures including single semiconductor epilayers, multiple quantum wells, and graphene-semiconductor heterostructures to develop coherent light sources and photodetectors in silicon. To develop coherent light sources, we reported the demonstration of room-temperature lasing at the technologically crucial 1.5 m wavelength range from Er-doped GaN epilayers and Er-doped GaN multiple-quantum wells grown on silicon and sapphire. The realization of room-temperature lasing at the minimum loss window of optical fiber and in the eye-safe wavelength region of 1.5 m is highly sought-after for use in many applications in various fields including defense, industrial processing, communication, medicine, spectroscopy and imaging. The results laid the foundation for achieving hybrid GaN-Si lasers providing a new pathway towards full photonic integration for silicon optoelectronics. Silicon photodiodes contribute a large portion in the photodetector market. However, silicon photodetectors are sensitive in the UV to near infrared region. Photodetection in the mid-infrared is based on thermal radiation detectors, narrow bandgap materials (InGaAs, HgCdTe) semiconductors, photo-ionization of shallow impurities in semiconductors (Si:As, Ge:Ga), and quantum well structures. Such technology requires complicated fabrication processes or cryogenic operation, resulting in manufacturing costs and severe integration issues. To develop broadband photodetectors, we focus on graphene photodetectors on silicon. Graphene generates photocarriers by absorbing photons in a broadband spectrum from the deep-ultraviolet to the terahertz region. Graphene can be realized as the next generation broadband photodetection material, especially in the infrared to terahertz region. Here, we have demonstrated high-performance hybrid photodetectors operating from the deep-ultraviolet to the mid-infrared region with high sensitivity and ultrafast response by coupling graphene with a p-type semiconductor photosensitizer, nitrogen-doped Ta2O5 thin film. / Doctor of Philosophy / According to Moor's law, the number of transistors per die area doubles every 18 months with no increase in power consumption, which means that digital devices including smart phones and computers will become significantly faster and more energy-efficient than those of the previous generation. Photons (light) travel with the highest speed permitted by the known law of physics. The idea of optical interconnects, using photons instead of electrons, enables faster data transfer. Two important elements of the integrated circuits (ICs) based on photons are the coherent light source (laser) and the photodetector. We investigated the optical properties of erbium doped gallium nitride epilayers and multiple quantum wells grown on silicon and sapphire and demonstrated lasing from these materials at 1.5 µm. We also fabricated and characterized graphene photodetectors that can detect the light from the deep ultraviolet to the mid-infrared region. The results provided a new pathway towards full photonic integration for silicon optoelectronics. Besides, they are the heart of many important applications ranging from gas sensing, aerospace sensors and systems, thermal imaging, biomedical imaging, infrared spectroscopy, and lidar-to-optical telecommunications.

Hydrothermal systems associated with oceanic spreading centers account for a quarter of Earth's total heat flux and one third of the heat flux through the ocean floor. Circulation of seawater through these systems alters both the crust and the circulating fluid, impacting global geochemical cycles. The warm vent fluids rich in nutrients support a wide variety of unique biological communities. Thus, understanding hydrothermal processes at oceanic spreading centers is important to provide insight into thermal and biogeochemical processes. In this dissertation I present the results of numerical modeling efforts for mid-ocean ridge hydrothermal systems. In the three manuscripts presented, permeability emerges as a key controlling factor for hydrothermal venting. In the first manuscript, I use 2-D numerical models to find that the distribution of permeability in the crust controls fluid velocity as well as the amount of mixing between hot hydrothermal fluids and cold seawater. This, in turn, effects the temperature and composition of fluids emerging on the surface. For the second manuscript, I construct single-pass 1-D models to show that a sudden increase in permeability caused due to magmatic or seismic events in the seafloor causes a sharp rise in the fluid output of the system. This, in conjunction with steep thermal gradients close to the surface, results in a rapid increase of venting temperatures. In the third manuscript, I develop a particle tracking model to study fluid trajectories in the subsurface. The results show that permeability distribution in the subsurface governs fluid paths and consequently, the residence time of fluids in the crust. Based on the work presented in this document, I conclude that permeability distribution, both local and field scale, exerts a major control on hydrothermal circulation in the subsurface and on the temperature and composition of venting fluids on the surface. / Ph. D.

Hydrothermal processes at oceanic spreading centers are largely influenced by changing magmatic heat input. I use the FISHES code to investigate the evolution of surface temperature and salinity as a function of time-varying heat flux at the base of a two-phase, vapor-brine hydrothermal system. I consider a two-dimensional rectangular box that is 1.5 km deep and 4 km long with homogeneous permeability. Impermeable, insulated conditions are imposed on the left and right hand boundaries. To simulate time-varying heat flux from a sub-axial magma chamber of 500 m long half-width, I consider a variety of basal boundary conditions: (1) a constant heat flux with an value of 130 W/m2; (2) a sinusoidal heat flux with a period of 6 years and an amplitude ranging between 100 and 50 W/m2; (3) step, random, and exponential heat fluxes ranging between 200 and 15 W/m2; and (4) an analytical function of temporally decaying heat flux resulting from a simulated cooling, crystallizing magmatic sill. As a result of the investigation I find: (1) changes in bottom temperature and salinity closely follow the temporal variations in magmatic heat inputs; (2) the surface temperature response is severely damped and high frequency variations in heat flow are not detected; (3) in regions where phase separation of vapor and brine occurs, surface salinity variations may be recorded in response to changing conditions at depth, but these are smaller in amplitude. / Master of Science