No / In recent years there has been growing interest in the use of noise barrier profiles that can enhance the diffraction efficiency of plane barriers. These are placed on the top of the barrier in order to reduce sound diffracted into the shadow zone. A variety of shapes have been tested including T-shapes, multiple-edges and various cylindrical configurations. Despite numerous demonstrations that the profiles enhance performance there is no universal agreement on how the improvements can be quantified and incorporated into noise prediction models. Without such quantification it is likely that such profiles will not receive widespread acceptance. TRL has carried out an experimental investigation of the performance of novel-shaped barriers for the Transport Research Foundation. The approach relies on quantifying diffraction efficiency in the near field using a novel application of the Maximum Length Sequence (MLS)-based method. Measurements on 4 different profiles were taken in the vertical plane perpendicular to the barrier face. Two source and four receiver positions were used and results were obtained under a range of wind conditions. Results show large differences between the efficiency of the different options with the absorptive T-shaped and multiple-edge profiles performing best.

The blood-brain barrier (BBB) is composed of brain microvascular endothelial cells (BMECs), pericytes, and astrocytic endfeet, which regulate the transport of molecules into and out of the brain. BMECs possess intrinsic barrier properties that limit the passage of approximately 98% of small molecules into the brain in healthy individuals. However, in some brain diseases, the BBB undergoes structural and functional alterations, which can contribute to disease progression. In this study, we aimed to investigate the BBB by exploring the effects of endothelial cell stretching and the optimal dimensionality of stretching to enhance endothelium barrier tightness in Chapter 2. Subsequently, we developed an endothelium gradient stretching device to further examine the stretching effect in Chapter 3. Additionally, we investigated the promotion of endothelium tightness through the use of electrospun fibers, wherein we controlled the pore size. Based on these findings, we designed and fabricated an organ chip model that incorporates mechanical stretching, microfluidic techniques, electrospun fibers, and hydrogel extracellular matrix (ECM). The results of permeability testing demonstrated that this chip significantly improved the tightness of microvascular selective transport ability and has the potential to be used in drug sorting for central nervous system (CNS) diseases.

Ceramics have a wide variety of applications due to their unique properties; however, the low fracture toughness leads the formation and propagation of unpredictable cracks, and reduces their reliability. To solve this problem, self-healing adaptive oxides were developed. The aim of the work is to gain new insights into self-healing mechanisms of ceramics and their application. Binary oxide systems were investigated that are at least partially healed through the extrinsic or intrinsic addition of silver or silver oxide to form ternary oxides (e.g., Nb2O5 + Ag → AgNbO3). Sintered pellets and coatings were tested. For self-healing TBCs, model systems that were studied include YSZ-Al2O3-SiC, YSZ-Al2O3-TiC, YSZ-Al2O3-Nb2O5, and YSZ-Al2O3-Ta2O5. Laser cladded samples and sintered pellets were produced to test. The healing process occurs due to the formation of oxidation products and glassy phases depending on the self-healing mechanism. X-ray diffraction was used to explore phase evolution, chemical compositions, and structural properties of these samples. SEM equipped with EDS was used to investigate the chemical and morphological properties for the cross-sectional area. Pin-on-disc test was applied to test tribology performance for Nb2O5-Ag2O system, and infiltration test was applied to test CMAS-resistance for TBCs at elevated temperature. The improvements in the performance of these materials were demonstrated.

This work demonstrates how local, randomized tailoring of bond stiffness can affect the activation energy of diffusion in model alloys using density functional theory-based computations. This work is organized into two parts. The first part deals with the vacancy diffusion mechanism, and it compares the in–plane (IP) vs out-of-plane (OOP) diffusion paths in prototypical binary Mg-X (Ca, Y, and Gd) and ternary Mg-X (Ca, Y, and Gd)-Zn alloys. We examine how vacancy formation, migration, and solute vacancy binding energies in binary Mg-X alloys influence diffusion activation and correlated them with conventional diffusion model based solely on the solute sizes. Next, we explore how Zn addition to binary Mg-X (Ca, Y, and Gd) alloys influences the OOP activation energy barrier is discussed in terms of detailed energetic computations and bond characterization in the present work. Our results indicate that Zn addition further enhances the OOP activation energy barrier compared to corresponding activation energies in Mg binaries. This work concludes that engineering stiffer directional bonds via micro-alloying additions in Mg is a promising route to dramatically improve their high temperature creep response. The second part of my work investigates the effects of Si, P, and S solutes on H interstitial diffusion mechanism in Ni. It examines how H interacts with vacancy, impurity atom, and vacancy-impurity atom defect pair by performing binding energy calculations. Results indicate that vacancy-impurity atom defect pair strongly traps the H atom compared to isolated defects. Finally, the effect of impurities on activation energy barrier of H diffusing in Ni is discussed by correlating migration energetics with bonding characteristics by performing charge density and electron density calculations. Our study validates experimental hypothesis of Berkowitz and Kane which postulates that P enhances the H diffusion in Ni. The present work also shows that H diffusion speeds up in Ni in the presence of Si and S solutes. In conclusion, we show that micro-alloying additions induce local lattice level pockets with covalent character, which substantially enhances the local bond stiffness. This will increase activation energy for vacancy diffusion mechanism while it reduces activation energy for interstitial H diffusion.

Traumatic brain injury (TBI) is the signature injury of modern military conflicts due to widespread use of improvised explosive devices (IEDs) and modern body armor. However, the exact biophysical mechanisms of blast-induced traumatic brain injury (bTBI) and its pathological effects on the blood-brain barrier (BBB) – a structure essential for maintaining brain homeostasis – remain poorly understood. The specific aims of this thesis are to: 1) determine a threshold for primary blast-induced BBB dysfunction in vitro; 2) determine the effect of repeated blast on BBB integrity in vitro; 3) improve BBB recovery in vitro as a potential therapeutic strategy for mitigating effects of blast; and 4) quantify the time course and pore-size of BBB opening in vivo. In this work we utilized a shock tube driven by compressed gas to generate operationally relevant, ideal pressure profiles consistent with IEDs. By multiple measures, the barrier function of an in vitro BBB model was disrupted after exposure to a range of blast-loading conditions. Trans-endothelial electrical resistance (TEER) decreased acutely in a dose-dependent manner that was most strongly correlated with impulse, as opposed to peak overpressure or duration. Significantly increased hydraulic conductivity and solute permeability post-injury further confirmed acute alterations in barrier function. Compromised ZO-1 immunostaining identified a structural basis for BBB breakdown. These results are the first to demonstrate acute disruption of an in vitro BBB model after primary blast exposure; defined tolerance criteria may be important for development of novel helmet designs to help mitigate effects of blast on the BBB. After determining that exposure to a single primary blast caused BBB disruption, we hypothesized that exposure to two consecutive blast injuries would result in exacerbated damage to the BBB in vitro. However, contrary to our hypothesis, repeated mild or moderate primary blast delivered within 24 or 72 hours did not significantly exacerbate reductions in TEER across a brain endothelial monolayer compared to sister cultures receiving a single exposure. Single blast exposure significantly reduced immunostaining of ZO-1 and claudin-5 tight junction proteins, but subsequent exposure did not cause additional damage to tight junctions. The second injury delayed recovery of TEER and hydraulic conductivity in BBB cultures. Extending the inter-injury interval to 72 hours, the effects of repeated injury on the BBB were independent given sufficient recovery time between consecutive exposures. Investigation of repeated blast on the BBB will help identify a temporal window of vulnerability to repeated exposure. Restoration of the BBB after blast injury has emerged as a promising therapeutic target. We hypothesized that treatment with dexamethasone (DEX) after primary blast would potentiate recovery of an in vitro BBB model. DEX treatment resulted in complete recovery of TEER and hydraulic conductivity 1 day after injury, compared with 3 days for vehicle-treated injured cultures. Administration of RU486 (mifepristone) inhibited effects of DEX, confirming that barrier restoration was mediated by glucocorticoid receptor signaling. Potentiated recovery with DEX treatment was accompanied by stronger ZO-1 tight junction immunostaining and expression, suggesting that increased ZO-1 expression was a structural correlate to BBB recovery. This is the first study to provide a mechanistic basis for potentiated functional recovery of an in vitro BBB model due to glucocorticoid treatment after blast injury. Using an in vivo bTBI model, systemic administration of sodium fluorescein (NaFl; 376 Da), Evans blue (EB; 69 kDa when bound to serum albumin) and dextrans (3 – 500 kDa) was used to estimate the pore-size of BBB opening and time required for recovery. Exposure to blast resulted in significant acute extravasation of NaFl, 3 kDa dextran, and EB. However, there was no significant acute extravasation of 70 kDa or 500 kDa dextrans, and minimal to no extravasation of NaFl, dextrans, or EB 1 day after exposure. This work is the first to quantify the time course and size of BBB opening after bTBI, suggesting that the BBB recovered 1 day post-injury. This study supports our hypothesis that transient opening of the BBB may permit serum-components to infiltrate the brain parenchyma and contribute to pathological secondary cascades. This research has shown that BBB damage, demonstrated in vitro and in vivo, is a major mechanism contributing to vascular and neuronal pathology of bTBI at exposure levels above a critical threshold. Compared with published studies on blast-induced damage to the BBB, we have developed primary blast injury tolerance criteria by precisely controlling the biomechanical initiators of injury and measuring resulting alterations to the structure and function of an in vitro BBB model by methods not possible in vivo. We have also developed a potential glucocorticoid treatment to rapidly restore the BBB after injury, which may lead to more promising therapeutic strategies to treat TBI-related pathologies. This work will also guide the development of novel armor designs to protect service members and civilians in order to more effectively address the burden to society of bTBI.

Given the increasing number of Chinese international students attending American universities, an important study would be to consider problems arising during these students' initial transition period, as they acculturate into the American culture and educational system. Taking this information into account, university counseling centers, campus services, and those who interact with and support these students would be better able to assist in easing the initial and ongoing stress of living in a foreign country and adapting to a new way of life. Thirteen Chinese international students participated in qualitative interviews conducted in Mandarin Chinese, each participant's native language. Each participant was born and raised in mainland China, had never travelled to the US before studying abroad, had no direct family relative in the US, and had studied at a university in the US for more than two years. In order to gain a better understanding of Chinese international students' initial transition to live and study in the US, a qualitative research design was utilized. This study used a collaborative hermeneutic approach to obtain a valid and common understanding of the meaning of each transcribed interview. Data analysis followed the hermeneutic circle, which emphasizes that the meaning of the text can be better understood through reading individual parts and comparing meanings of parts and whole. These study used a team to analyze data, thus avoiding the narrow reliance on individual interpretations. Based on their personal perspectives, participants reported their experiences encountered during their initial transition into the US. More specifically, information shared during individual interviews with Chinese international students indicated specific experiences in regard to their initial and ongoing adjustment to the U.S. environment, including how they made sense of their experiences and how their ways of thinking and behaving changed as a result of being influenced by their experiences interfacing with U.S. culture. Participants also shared their strategies they perceived as helpful in specific situations. Based on an analysis of participants interviews, themes that arose from the interviews included (a) difficulties and challenges they faced as new immigrants; (b) differences they encountered in respect to their homeland and the new environment, including language/communication, culture, academic study and learning, living in the US, and psychological adjustments; (c) positive growth they acknowledged from facing challenges and adapting to their new environment; and (d) acknowledging the need to accept help and how to more proactively seek and receive help as needed. Implications for more actively assisting and including Chinese international students are discussed.

Because of their good mechanical resistance at high temperature, Ni-based superalloys are used for aero-engine and land-based turbines but undergo "dry" oxidation between 900 and 1500°C. These materials are thus coated with nickel-aluminide coatings (BC). An additional thermal barrier coating (TBC) is generally applied in the hottest sections of the turbines (T>1050°C) to lower the impact of the temperature on the substrate. In the framework of the European research programme "PARTICOAT", this PhD work was focused on the growth mechanisms of a full protective coating system (BC+TBC) in a single step process, using a water-based slurry containing a dispersion of Al micro-particles to satisfy the European environmental directives. The rheological and physico-chemical characterizations showed the slurry stability up to seven days. After depositing the latter by air spraying, a tailored thermal treatment resulted in a nickel-aluminide coating (β-NiAl) similar to the conventional industrial ones but through an intermediate Al liquid phase stage. Simultaneously, the oxidation of the Al micro-particles brought aboutthe formation of a top alumina "foam" (PARTICOAT concept). After a validation step of the mechanisms involved in pure Ni substrate, the extrapolation of the process to several Ni-based superalloys (René N5 (SX), CM-247 (DS), PWA- 1483 (SX) and IN-738LC (EQ)) revealed different coating compositions and microstructures. A particular attention was therefore paid onto the effect of alloying elements (Cr, Ta, Ti) as well as their segregation in the coating. The high temperature behaviour of the coated samples has been studied through isothermal oxidation (1000h in air between 900 and 1100°C) and showed that the oxidation and interdiffusion phenomena ruled the degradation mechanisms. Besides, the electrodeposition of ceria before the application of the PARTICOAT coating allowed to strongly limit interdiffusion phenomena and stabilized the nickel aluminide coating.

Thesis (doctoral)--Universitetet i Lund. / Reprints of journal articles inserted in pocket inside back cover.

Thesis (M. Arch.)--University of Hong Kong, 2002. / Includes special report study entitled: Architecture and orientation & mobility training. Includes bibliographical references.

Thesis (Ph. D.)--West Virginia University, 2009. / Title from document title page. Document formatted into pages; contains xi, 165 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 131-163).