3D Printing of Hybrid Architectures via Core-Shell Material Extrusion Additive Manufacturing

Biological materials often employ hybrid architectures, such as the core-shell motif present in porcupine quills and plant stems, to achieve unique properties and performance. Drawing inspiration from these natural materials, a new method to fabricate lightweight and stiff core-shell architected filaments is reported. Specifically, a core-shell printhead conducive to printing highly loaded fiber-filled inks, as well as a new low-density syntactic foam ink, are utilized to 3D-print core-shell architectures consisting of a syntactic epoxy foam core surrounded by a stiff carbon fiber-reinforced epoxy composite shell. Effective printing of test specimens and structures with controlled geometry, composition, and architecture is demonstrated with printed core-shell samples exhibiting up to a 25 percent increase in specific stiffness over constituent materials. A detrimental increase in foam density was observed during initial core-shell printing due to failure of glass microballoons (GMBs) during extrusion. To solve this, the second part of the dissertation investigates the relationships between GMB loading, extrusion pressure, nozzle diameter, and flowrate on printed density. These parameters are investigated to gain understanding of the conditions leading to GMB failure, informing selection of process parameters to minimize it. A new syntactic foam ink is formulated with GMBs that exhibit a lower average diameter and higher crush strength, ultimately enabling printing without prominent GMB failure and the ability to achieve near theoretical printed density. The new foam samples are stronger and stiffer than conventional syntactic foams and current DIW-printed foams. Further implementation of the new foam in the C-S architecture enabled a 5 percent increase in specific stiffness over previous values. In the last study, work is done to further expand the capability of C-S printing by demonstrating multimaterial 3D printing using the core-shell nozzle. This approach enables “on-the-fly” switching between materials during fabrication, without the need for two nozzles. Material transition behavior is analyzed, multimaterial components are successfully printed, and flexural testing is conducted. Overall, the new approach enables material switching with a continuous print path, providing greater design flexibility and compositional control, opening new routes to DIW print multimaterial architectures

Protective Coating of Titanium Diboride Reinforcement Particulates for Improvement of Titanium Metal Matrix Composite Armor Systems

Titanium and titanium diboride (TiB2) are two materials that have attracted interest for application in armor systems. Titanium exhibits a high strength-to-weight ratio and good corrosion resistance while TiB2 exhibits high hardness and stiffness. Combining these into a titanium metal matrix composite would allow the superior ballistic properties to be taken advantage of in one composite material and lead to an improved armor system. The main obstacle behind doing so is the detrimental in situ reaction during processing between the Ti matrix and the TiB2 reinforcing particles that converts TiB2 into TiB. It was hypothesized that a protective coating on the TiB2 particulates would protect and prevent the in situ reaction. Two protective designs were investigated: depositing a carbon layer on the particle surface and also nitrogenizing the particle surface to create a boron nitride (BN) coating. TiB2 particulates were coated using fluidized bed chemical vapor deposition. Powders were blended and then produced either by pressing and firing or by hot pressing. Three separate experiments were performed: variable time, variable temperature, and hot pressing experiments. Samples were characterized using X-ray diffraction and microscopy focusing on phase identification and the coating’s effectiveness in preventing TiB formation. Impact testing using half-size charpy bars cut from the hot pressed plate samples also allowed investigation of impact behavior. The nitrogenizing of the particle surface was shown to be unsuccessful in preventing the conversion of TiB2 into TiB. Reaction between the Ti matrix and TiB2 readily occurs if the particles are not coated. The carbon coating was proven successful in preventing the conversion of TiB2 particles into TiB up to dwell times of 2 h at 1370 °C while also providing complete protection in a sample hot pressed at 1200°C. The carbon coating design presented was proven successful through a range of processing conditions in preventing the in situ conversion of TiB2 into TiB providing a route to produce a metal matrix composite wherein the TiB2 reinforcing particles remain intact and unconverted after processing. This material could lead to the production of an improved armor system

Foreign direct investment and spillovers : gradualism may be better

The definitive version is available at www3.interscience.wiley.comThe standard argument says that in the presence of positive spillovers foreign direct investment should be promoted and subsidized. In contrast, this paper claims that the very existence of spillovers may require temporarily restricting FDI. Our argument is based on two features of spillovers: they are limited by the economy's absorptive capacity and they take time to materialize. By letting in capital more gradually, initial investment has the time to create spillovers – and upgrade the economy's absorptive capacity – before further investment occurs. The economy converges to a steady state with a superior technology and a greater capital stockPublicad

SINMAP 2.0 - A Stability Index Approach to Terrain Stability Hazard Mapping, User\u27s Manual

SINMAP 2.0 (Stability Index MAPping) is an ArcGIS 9.0 plug-in that implements the computation and mapping of a slope stability index based upon geographic information, primarily digital elevation data. This report describes the theoretical basis for the calculation of the stability index, describes the implementation, presents several case studies and describes use of the accompanying software. SINMAP has its theoretical basis in the infinite plane slope stability model with wetness (pore pressures) obtained from a topographically based steady state model of hydrology. Digital elevation model (DEM) methods are used to obtain the necessary input information (slope and specific catchment area). Parameters are allowed to be uncertain following uniform distributions between specified limits. These may be adjusted (and calibrated) for geographic ccalibration regionsd based upon soil, vegetation or geologic data. The methodology includes an interactive visual calibration that adjusts parameters while referring to observed landslides. The calibration involves adjustment of parameters so that the stability map ccapturesd a high proportion of observed landslides in regions with low stability index, while minimizing the extent of low stability regions and consequent alienation of terrain to regions where landslides have not been observed. This calibration is done while simultaneously referring to the stability index map, a specific catchment area and slope plot (of landslide and non landslide points) where lines distinguish the zones categorized into the different stability classes and a table giving summary statistics. The current implementation of SINMAP 2.0 is a plug-in to the ArcGIS ArcMap geographic information system (GIS) from Environmental Systems Research Institute, Inc. (ESRI). This utilizes ArcMap for its standard GIS functionality such as the input and organization of data and the presentation and output of results. SINMAP is grid based, requiring ArcGIS version 9.0 or higher

The Health Belief Model And Factors Relating To Potential Use Of A Vaccine For Shigellosis In Kaeng Koi District, Saraburi Province, Thailand

Shigellosis is an important cause of morbidity and mortality throughout the world. Approximately, 1.1 million deaths occur a year due to this disease, making it the fourth leading cause of mortality worldwide. This paper explores local interest in and potential use of a vaccine for shigellosis in Thailand where Shigella poses an important public-health concern. Data for this study were collected during June- November 2002 from 522 subjects surveyed using a sociobehavioural questionnaire in Kaeng Koi district in central Thailand. The community demand and likely use of a vaccine were examined in relation to the Health Belief Model, which provides analytical constructs for investigating the multiple issues of local readiness to accept and access a new vaccine. As the key outcome variable, most respondents showed interest in receiving a vaccine against dysentery which they thought would provide useful protection against the disease. However, there was only a moderate number who perceived dysentery as serious and themselves as susceptible to it, although it was perceived to cause some burden to and additional expense for families. Most people identified a number of groups who were thought to be especially vulnerable to dysentery, such as the elderly, pre-school, and school-age children, and poor labourers. Other outcomes of the study included the identification of acceptable and convenient sites for its delivery, such as government health clinics and private clinics, and respected sources for information about the vaccine, such as health clinic personnel and community health volunteers. This information suggests that components of the Health Belief Model may be useful in identifying community acceptance of a vaccine and the means of introducing it. This health information is important for planning and implementing vaccine programmes. Key words: Dysentery, Bacillary; Shigella; Bacterial vaccines; Health Belief Model; Perceptions; Cross-sectional studies; Thailan

An Undergraduate Curriculum in Public Health Benchmarked to the Needs of the Workforce

East Tennessee State University (ETSU) has offered an undergraduate degree in public health for 60 years. Alumni survey data have documented that the majority of the graduates from this program enter the workforce [see accompanying commentary by Wykoff, et al. (1)]. To keep pace with ongoing changes in the workforce, the decision was made to completely review, and, as appropriate, revise and restructure the Bachelor of Science in Public Health (BSPH) curriculum

Differences in perception of dysentery and enteric fever and willingness to receive vaccines among rural residents in China.

BACKGROUND: Enteric diseases including dysentery and enteric fever remain significant public health problems in China. While vaccines offer great potential in controlling these diseases, greater understanding of factors influencing acceptance of vaccines is needed to create effective enteric disease control programs in rural China. DESIGN: Cross-sectional quantitative study with randomly sampled households from two sites in China, one experiencing high rates of shigellosis (Zengding) and the other of typhoid/paratyphoid (Lingchuan). METHODS: Sociobehavioral survey data were collected through face-to-face interviews from 501 respondents (56% female) in Zhengding regarding dysentery and 624 in Lingchuan (51% female) regarding enteric fever. Vaccine acceptability was measured by expressed need for vaccination and willingness to pay. Comparative and associative analyses were conducted to assess disease perception, vaccination service satisfaction, likelihood of improvements in water and sanitation, and vaccine acceptability. RESULTS: Nearly all respondents in Lingchuan considered enteric fever to be prevalent in the community, while only one half of the respondents in Zhengding considered dysentery to be problematic (p < 0.01). Nevertheless, more respondents in Zhengding were fearful that a household member would acquire dysentery than were Lingchuan respondents worried that a household member would acquire enteric fever (p < 0.01). Perceived vulnerability of specific subgroups (odds ratios ranging from 1.6 to 8.1), knowing someone who died of the disease (odds ratio reached infinity) and satisfaction with past vaccination services (odds ratios reached infinity) were consistently associated with perceived need for vaccines of target populations of all age groups while the association between perception of sanitary improvement and vaccine need was limited. Perceived need for a vaccine was associated with willingness to pay for the vaccine. CONCLUSIONS: Perceptions of enhanced vulnerability of specific subgroups to a disease and satisfactory experiences with vaccination services may increase the perceived need for a vaccine, leading to increased willingness to pay for vaccine. Vaccines are not perceived as important for the elderly