Flow and thermal transport in additively manufactured metal lattices based on novel unit-cell topologies

The emergence of metal Additive Manufacturing (AM) over the last two decades has opened venues to mitigate the challenges associated with stochastic open-cell metal foams manufactured through the traditional foaming process. Regular lattices with user-defined unit cell topologies have been reported to exhibit better mechanical properties in comparison to metal foams which extend their applicability to multifunctional heat exchangers subjected to both thermal and mechanical loads. The current study aims at investigating the thermal-hydraulic characteristics of promising novel unit cell topologies realizable through AM technologies. Experimental investigation was conducted on four different topologies, viz (a) Octet, (b) Face-diagonal (FD) cube, (c) Tetrakaidecahedron, and (d) Cube, printed in single-cell thick sandwich type configuration in 420 stainless steel via Binder Jetting technology at same intended porosity. The effective thermal conductivity of the samples was found to be strongly dependent on the lattice porosity, however, no significant dependence on the unit-cell topology was demonstrated. Face-diagonal cube lattice exhibited the highest heat transfer coefficient and pressure drop, and consequently provided the lowest thermal-hydraulic performance. A procedure to incorporate the manufacturing-induced random roughness effects in the samples during numerical modelling is introduced. The numerical simulations were conducted on samples exhibiting the roughness profiles having statistically same mean roughness as the additively manufactured coupons and the results were compared to that obtained from the intended smooth-profiled CAD models that were fed into the printing machines. The analysis showed that inclusion of roughness effects in computational models can significantly improve the thermal performance predictions. Through this study, we demonstrate that additively manufactured ordered lattices exhibit superior thermal transport characteristics and future developmental efforts would require extensive experimentations to characterize their thermal and flow performance as well as local surface quality and AM-induced defect recognition. Experimental findings would also need to be supported by computational efforts where configurations which closely mimic the real AM parts could be modeled. A combined experimental-numerical framework is recommended for advancements in metal additive manufacturing-enabled enhanced heat transfer concepts

W.M. Keck 2012 Annual Report: Detection

This annual report includes a letter from the chairman, highlights of research directions, strategies and opportunituies presented at the Imaging and Detection of Single Molecules Workshop, details of grantmaking activities, financial statements, and a list of members and boardmembers

Optical Shaping of Structural Self-Oraganization and Topology in Soft Matter

The study of liquid crystals has brought about many advances and innovations, not only in technology, but also in our basic understanding of the world around us. For example, recent explorations of photo-induced defects and colloidal clusters in chiral nematics reveal topologically nontrivial forms in liquid crystal director fields, such as localized field structures resembling the Hopf and Seifert fibrations. In this work, we use light to control the alignment of liquid crystal director field at surfaces, to define topologically nontrivial geometric shapes of colloidal particles, and to probe the interplay between the topology of defects, director fields and surfaces. We first explore photo-responsive, azobenzene-based surface monolayers as means to optically and dynamically control boundary conditions at liquid crystal interfaces. This enables us to induce localized regions of twisted nematic field and disclination loops, which interact elastically with particle inclusions, providing a new kind of long-range, low-power colloidal manipulation as well as a means for controlling large-scale dynamics of topological defects and colloids. Using this same surface control technique, we pattern topological defects into thin films of polymerized liquid crystals, also functionalized with azobenzene. Irradiation of these films causes internal mechanical stresses that induce changes in the films' topography, depending on the patterned topology of the internal field structure within the photoresponsive liquid crystal polymer. We then employ a two-photon photo-polymerization technique to fabricate chiral, knotted and linked polymer microstructures, which we introduce into nematic liquid crystals. Based on three-photon excitation fluorescence polarizing microscopy studies, we reconstruct the surrounding 3D director field structure, revealing induced chiral, knotted and linked defect lines and fields. Using videomicroscopy, we characterize the inter-particle elastic forces that govern long range interactions and stabilize self-assembled colloidal configurations. Since there are few examples of practical realization of topological field configurations, these knotted and inter-linked colloids and fields provide a way to gain insights into behavior of other experimentally less accessible physical systems with similar symmetry and topology. Throughout the thesis, my research demonstrated that the topology of soft condensed matter can be shaped by light, laying a groundwork for experimental exploration of low-dimensional topology of fields and surfaces as well as for practical applications of topological relations in designing new forms of self-assembly

Ordovician corals of the Williston Basin periphery

Tabulate and rugose corals are described from the Ordovician Red River) Stony Mountain, and Stonewall Formations in southern Manitoba and the Ordovician Bighorn Formation in northern Wyoming. Fifty-four species, 12 of which are new, are distributed in 20 genera. The Flower Model of coral evolution, based on wall microstructure of colonial corals, is extended to include the septa! Microstructure of colonial and solitary corals. Primitive corals are characterized by non t-rabeculate walls and septa whereas advanced forms are characterizedby trabeculate walls and septa. Mid-range corals are those with intermediate stages of trabecular development in walls .and septa. Corals in the Red River Formation are primarily colonial, primitive , and mid-range, and are geographically widespread) ranging from New Mexico to Greenland in a northeast-southwest trending belt defining an Ordovician equatorial realm, but rarely occurring elsewhere in North America. Solitary corals in the Red River fauna were ancestral to those in the Stony Mountain fauna, but the colonial forms in the Red River Formation were not ancestral to those in the Stony Mountain. Corals in the Stony Mountain and Stonewall Formations in Manitoba and the faunas in the Bighorn Formation in northern Wyoming are younger, considerably more advanced, and geographically more restricted than those in the Red River. The colonial corals are predominant in carbonate rocks whereas the solitary corals are most abundant in argillaceous carbonates and argillites, implying intolerance of the colonial forms for terrigenous elastics. The solitary forms were apparently not as efficient as the colonial corals in utilizing available energy under conditions of carbonate sedimentation. A paraconformity in the subsurface of northeastern North Dakota and diastems in the type section of the Fort Garry Member of the Red River Formation indicate that the cratonic platform east of the Williston Basin was e:x:posed for part or all of the time the evaporitic upper Red River11 was being deposited in the Basin. The paraconformity occupies the same stratigraphic position as the Fort Garry Member, the upper Red River and an unconformity traceable from New Mexico to the Hudson Bay region. Corals below this paraconformity and the Fort Garry are mostly primitive whereas those above them are advanced. Paleofavosites has its lowest stratigraphic occurrence in the Fort Garry Member. The Cat Head Member of the Red River Formation does not extend southward into northeastern North Dakota and is a dolomitized version of the underlying Dog Head Member. Some corals are useful for correlation of Ordovician rocks from New Mexico to Greenland and reflect relatively uniform. Environmental conditions in the Ordovician equatorial realm but are not effective for correlation outside the realm. The widespread occurrence of Paleofavosites in and outside the areas of study, the change from nontrabeculate to trabeculate septa in some solitary corals, and the primitive versus advanced characters of the coral faunas may be of future use for correlation and age determination in and outside the realm

Molecular Identification And Analysis Of Treponematosis (Syphilis, Bejel, Yaws, Or Pinta) In Ancient Mummified Remains From Northern Chile And Southern Peru

Thesis (Ph.D.) University of Alaska Fairbanks, 2008The sequencing of Treponema pallidum subsp. pallidum, the bacterium that causes syphilis, and the identification of a family of 12 genes with sequence similarity that allows scientists to distinguish between treponemal subtypes has opened up a new line of inquiry for biological anthropologists. This research contributes genetic evidence of pre-contact treponematosis in the Americas; by combining osteological and molecular evidence with data on environment and cultural practices, it also furthers our knowledge of human-pathogen interaction. This research assessed the presence of treponematosis, a bacterial spirochete, in the DNA of skeletal and mummified human remains from northern Chilean cemeteries dating from 5000 BC to AD 1100. The objectives were to: (1) determine whether treponemal DNA could be successfully recovered, amplified, and identified by subspecies from ancient bone and tissue, (2) compare any ancient sequences generated to the modern strains present in the National Center for Biotechnology Information (NCBI) GenBank database, (3) test the null hypothesis that treponematosis was not present in the New World before European contact, and (4) explore which cultural factors may have contributed to the spread of treponematosis in these groups. This research established a foundation for future treponemal studies through the development of primers and protocols for the analysis of ancient treponemes. The results of this study suggest that the inhabitants of this region suffered from a systemic bacterial infection, likely a chronic form of non-venereal treponematosis: yaws or bejel. Potential treponemal DNA was recovered from bone in an individual dated 202 cal BC--cal AD 3 from the Azapa valley. An investigation of Chinchorro artificial mummification suggests that their mortuary practice likely did not result in a higher frequency of treponematosis, as compared to later and inland groups. Rather, status and socioeconomic factors may have played a role in differential infection rates between those mummified in complex styles and those in natural or less complex styles. Further analysis of human remains with suspected treponemal lesions is necessary to reconstruct the history of treponematosis, improve our understanding of their pathogenesis, and guide scientists in developing preventative measures

(I) Polymer Nanocomposites: Rheology and Processing for Mesoporous Materials and (II) Nanopatterning of Metal Oxides Using Soft Lithography

The research in this dissertation is categorized into two parts. The first part is focused on investigation of order-to-disorder transitions (ODT) in nanocomposites of an amphiphilic block copolymer containing various hydrogen-bonded additives, and fabrication of novel mesoporous silica based materials by utilizing such nanocomposites as templates. Disordered Pluronic®, poly(ethylene oxide) (PEO)−poly(propylene oxide) (PPO)−PEO triblock copolymer upon blending with small molecule additives containing hydrogen-bond-donating functional groups (carboxyl or hydroxyl) result into ordered nanoscale morphologies by preferentially interacting with the hydrophilic PEO chains in the Pluronic®. The dependence of ODT-temperature in these novel Pluronic®/small-molecule-additive complexes on composition, number and type of functional groups on the additive, and the phase behavior of complexes, is explored using rheology. High loadings of metallic nanoparticles can be achieved in the hydrophilic PEO domain of the Pluronic® by taking the advantage of hydrogen bonding interactions. By utilizing Pluronic®/nanoparticle composites as templates, well-ordered mesoporous/nanoparticle composites (with up to 15 wt% nanoparticles) are fabricated using supercritical carbon dioxide (scCO2)assisted infusion and phase selective condensation of a silica-precursor within the PEO phase of the template. Well-ordered mesoporous silica with such high concentrations of uniformly distributed nanoparticles are advantageous in catalysis, but are elusive using synthetic routes explored in the literature. Hierarchically porous silica monoliths with high surface area mesopores interconnected through macropores are fabricated using scCO2 assisted phase selective infusion and condensation of a silica-precursor in a Pluronic®/small-molecule-additive template coated on a macroporous template. The surface area of mesoporous silica prepared by the scCO2 infusion process is reported for the first time using nitrogen physisorption experiments. A systematic study of various parameters pertaining to the scCO2 infusion process on the final morphology and surface area of the mesoporous silica is carried out. In the second part, a soft lithography technique is explored to fabricate nanostructures of inorganic oxides, for example ITO and TiO2,using inks containing crystalline nanoparticles. The technique is evaluated based on its ability to imprint dimensionally stable high-aspect-ratio nanostructures. Rapid imprinting, residual-layer free imprinting and imprinting of sub-200-nm structures is also demonstrated. A layer-by-layer imprinting strategy is developed to realize all-solution processable 3D inorganic nanostructures

Vorticity structure and evolution in a transverse jet with new algorithms for scalable particle simulation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.Includes bibliographical references (p. 188-200).Transverse jets arise in many applications, including propulsion, effluent dispersion, oil field flows, V/STOL aerodynamics, and drug delivery. Furthermore, they exemplify flows dominated by coherent structures that cascade into smaller scales, a source of many current challenges in fluid dynamics. This study seeks a fundamental, mechanistic understanding of the relationship between the dispersion of jet fluid and the underlying vortical structures of the transverse jet-and of how to develop actuation that optimally manipulates their dynamics to affect mixing. We develop a massively parallel 3-D vortex simulation of a high-momentum transverse jet at large Reynolds number, featuring a discrete filament representation of the vorticity field with local mesh refinement to capture stretching and folding and hair-pin removal to regularize the formation of small scales. A novel formulation of the vorticity flux boundary conditions rigorously accounts for the interaction of channel vorticity with the jet boundary layer. This formulation yields analytical expressions for vortex lines in near field of the jet and suggests effective modes of unsteady actuation at the nozzle. The present computational approach requires hierarchical N-body methods for velocity evaluation at each timestep, as direct summation is prohibitively expensive. We introduce new clustering algorithms for parallel domain decomposition of N-body interactions and demonstrate the optimality of the resulting cluster geometries. We also develop compatible techniques for dynamic load balancing, including adaptive scaling of cluster metrics and adaptive redistribution of their centroids. These tools extend to parallel hierarchical simulation of N-body problems in gravitational astrophysics,(cont.) molecular dynamics, and other fields. Simulations reveal the mechanisms by which vortical structures evolve; previous computational and experimental investigations of these processes have been incomplete at best, limited to low Reynolds numbers, transient early-stage dynamics, or Eulerian diagnostics of essentially Lagrangian phenomena. Transformation of the cylindrical shear layer emanating from the nozzle, initially dominated by azimuthal vorticity, begins with axial elongation of its lee side to form sections of counter-rotating vorticity aligned with the jet trajectory. Periodic rollup of the shear layer accompanies this deformation, creating arcs carrying azimuthal vorticity of alternating signs, curved toward the windward side of the jet. Following the pronounced bending of the trajectory into the crossflow, we observe a catastrophic breakdown of these sparse periodic structures into a dense distribution of smaller scales, with an attendant complexity of tangled vortex filaments. Nonetheless, spatial filtering of this region reveals the persistence of counter-rotating streamwise vorticity. We further characterize the flow by calculating maximum direct Lyapunov exponents of particle trajectories, identifying repelling material surfaces that organize finite-time mixing.by Youssef Mohamed Marzouk.Ph.D

THE USE OF STABLE ISOTOPE ANALYSIS ON BURIALS AT CAHAL PECH, BELIZE IN ORDER TO IDENTIFY TRENDS IN MORTUARY PRACTICES OVER TIME AND SPACE

The Late (AD 500-700) to Terminal (AD 700-900) Classic transition in the Maya Southern Lowlands has been defined as a period of decline and large scale migrations out of ceremonial centers. The reduced access to food due to multi-decadal droughts severely affected the social and political environments during this period. Previous research focused on large scale geographic migration and diet in this area. What is less understood is the degree and direction of migration at a site-specific level, as well as the community’s specific response through time. This research uses the human remains along with their associated mortuary artifacts from the site of Cahal Pech, Cayo District, Belize in order to understand one community’s response to environmental stress during the Late to Terminal Classic period. Several multivariate statistical analyses were run on a comprehensive stable isotope plan (δ13C, δ15N, δ34S, 86Sr/87Sr, and δ18O) and mortuary database for 27 individuals from the site core. These result were then compared to models created by the author in order to find a best fit. This research found that migration into and out of Cahal Pech was occurring at a similar rate over time and that almost all individuals that showed non-local isotope signatures came from the Macal River region south of the site. The mortuary patterns do not trend on time period, age and sex, origin of the individual, or location of the burial at the site. Rather, the mortuary patterns initially cluster based on grave type and presence or absence of certain grave goods. The findings show no effect during the transition from the Late to Terminal Classic based on the mortuary and bioarchaeological data. This unexpected result may be due to sampling only the Cahal Pech core, possibly representing elite individuals buffered from the worst effects of deteriorating environmental conditions. In order to understand if this is a unique occurrence or regionally expressed, future research will need to be undertaken with broader parameters