Investigation of Stacking Fault and Antiphase Boundary Segregation in Ni-Based Superalloys Using Density Functional Theory

Ni-base superalloys have a long history of use in jet turbine engines, and efforts to improve their performance in that application are ongoing. It is known that the precipitation of the Ni3Al ' phase within the disordered FCC phase strengthens the overall material. However, in the high-temperature environment found inside a turbine engine during operation, creep can cause the ' phase to transform to different, weaker phases along stacking faults, leading to a deterioration of performance. In the ' phase one mode of creep deformation is the formation of stacking fault ribbons, which consist of intrinsic stacking faults further shearing into antiphase boundaries (APBs). It is also known that certain alloying additions exhibit segregation to stacking faults. If segregating elements could be identified which segregate to the intrinsic stacking fault, but not to the APB, the inclusion of such elements could lead to improved creep strength in these alloys. To investigate this possibility, a density functional investigation of the segregation of W, Mo and Cr to both a superlattice intrinsic stacking fault (SISF) and an APB was performed. It was found that W, Mo and Cr all exhibit segregation to the SISF. In contrast, for the APB, Cr was either energy-neutral, or segregates, depending on the presence of additional nearby Cr, or on the specific lattice site upon which it was placed, while Mo and W did not segregate. Because W and Mo segregate to the SISF but not to the APB, the inclusion of these elements could provide a degree of protection against creep-related deterioration

Cold climate water/wastewater transportation and treatment - a bibliography: completion report

This bibliography contains 1,400 citations, including published and unpublished papers, on cold-climate water and wastewater transportation and treatment systems. Sources listed include state and federal agency files which contain information on systems in Alaskan communities and the Alyeska Pipeline Service Company camps. References to systems in other northern countries are also included. The objectives of this study were to identify causes of the failure of Alaskan water and wastewater treatment and transportation facilities and to seek methods for design improvements. Originally, the investigators contemplated an evaluation of systems performance in remote areas in relation to the original conception, planning, design, and construction. Because of the tremendous amount of literature examined, the evaluation was undertaken in a subsequent study, "Alaska Wastewater Treatment Technology" (A-058-ALAS) by Dr. Ronald A. Johnson.OWRT AGREEMENT NO. 14-31-0001-5002 PROJECT NO. A-047-ALAS The work upon which this completion report is based was supported by funds provided by the U. S. Department of the Interior, Office of Water Research and Technology, as authorized under the Water Resources Research Act of 1964, Public Law 88-379, as amended

Reproduction in South American Camelids

Six species of camels exist in the world today: the llama (Lama glama) and alpaca (Lama pacos) were domesticated in South America 4-5 thousand years ago, while the guanaco (Lama guanicoe) and vicuna (Vicugna vicugna) still exist in the wild. The more familiar bactrian camel (Camelus bactrianus) of Asia and the African dromedary camel (Camelus dromediarus) make up the balance of the camelids. The four species of South American camelids are ancestors of llama-like creatures that stalked North America in the Pliocene Epoch. As their resources depleted they moved south toward South America while their relatives, the camels, went east to Asia and Africa

Understanding Childhood Malnutrition in Nepal: A Hierarchical Regression Approach

This thesis investigates the determinants of childhood malnutrition in Nepal, with a particular emphasis on the importance of district characteristics relative to household and child characteristics. Using a new dataset constructed from child and household data from the 2006 and 2011 Nepal Demographic and Health Survey (DHS) and community characteristics aggregated from the 2004 and 2010 Nepal Living Standards Survey (NLSS), we estimate a variety of hierarchical regression models, which allow us to partition variance in height-for-age Z-scores between the levels of different hierarchical specifications, and then to partition that variance further, between group-level parameters. Our findings suggest that the majority of variance in HAZ occurs between children, though the vast majority of variance between districts can be partitioned into variances in agricultural input use and commercialization, healthcare access, and ethnic marginalization, combined with their estimated coefficients. The results generated by models designed to evaluate the robustness of the core estimation strategy also suggest that while variation among children is the largest source of variance, a small but nontrivial proportion of that variance is variance among households

Exploring Customer Value in the Hardwood Lumber Industry

In this paper, the author investigates the role of product, service, and price-relative to competition-in determining customer value perceptions among buyers of northern hardwood lumber. Based on survey data collected in December 1999, this study examines the importance of attributes affecting purchase decisions and compares these findings with a regression approach incorporating an explicit customer value measurement. These data indicate that attributes deemed important to the purchaser are not necessarily the same attributes related to perceptions of highly valued suppliers. Results indicate that consistent availability of desired species and aesthetic qualities of shipments are the most influential attributes in the identification of suppliers providing high levels of customer value. Finally, value perceptions are examined across broad industrial buyer segments

THE IMPACT OF AN AGING RURAL POPULATION ON LOCAL TAX STRUCTURES

The growing American retired population increasingly is viewed for its economic development potential. The relationship between the elderly and local taxes may have a critical effect on this potential, however. This paper examines the local tax implications of an increasing elderly population in communities prohibiting tax referenda. In such communities, citizens have no direct role in tax decisions. The elderly's attitudes towards different local taxes are examined using telephone survey data, before using aggregate data to investigate the relationship between the elderly and the specific taxes used in communities. The results suggest that a high proportion of elderly do not affect the mix of local taxes, but that an increasing proportion does have an influence.Community/Rural/Urban Development,

Identifying pathogenic Salmonella serotypes isolated from South Central VA waterways via sequential PCR analysis

Researchers often debate whether all serovars of Salmonella enterica are pathogenic to humans. Broiler houses containing chickens are a major source of Salmonella and serve as potential reservoirs. Therefore, farmers must take substantial measures in order to avoid contamination with their products. The primary objective of the study was to determine whether the four most clinically relevant Salmonella spp. serovars from poultry houses could be isolated from the environmental waterways in Prince Edward and Cumberland Counties of Virginia. The study adapted a serotyping method designed for typing Salmonella to gain a perspective of possible serovars that may be found in local waterways. All of the isolates tested positive in a latex solution to confirm the isolate as Salmonella spp presence. 15 out of the 32 isolates were typed to Group 1 Salmonella, which is most closely associated with human illness. Additionally, 13 isolates were able to be identified to one of the four targeted serovars. The four targeted serovars were Typhimurium, Enteritidis, Hadar, and Heidelberg. The study was not able to accurately serotype any of the aforementioned serovars

Producing Next Generation Superalloys Through Advanced Characterization and Manufacturing Techniques

NASA is currently working towards developing the next generation high temperature alloys for various aerospace and energy applications. Through advanced microscopy and computational insights, a novel atomic scale strengthening mechanism was discovered in Ni-base superalloys. This new local phase transformation strengthening technique has been successfully implemented resulting in new disk alloys with substantial improvements in creep strength over current state-of-the-art. Furthermore, additive manufacturing has been leveraged to produce dispersion strengthened (DS), multi-principal element alloys (MPEA) without the use of traditional mechanical alloying or chemical reactions. This new processing technique has successfully resulted in 99.9% dense oxide dispersion strengthened NiCoCr alloy parts. High temperature mechanical testing of the DS alloys showed significant improvements in strength and ductility over the baseline NiCoCr. As a result, this recently discovered processing route opens a new alloy design and production path that is synergistic between additive manufacturing and dispersion strengthening, possibly enabling a new generation of high-performance alloys

Battling on the Home Front: Posttraumatic Stress Disorder and Conflict Behavior Among Military Couples

This study evaluated interpersonal behavior differences among male military service members with and without PTSD and their female partners. Couples (N = 64) completed a 17-minute videotaped conflict discussion, and their interaction behavior was coded using the circumplex-based Structural Analysis of Social Behavior model (SASB; Benjamin, 1979, 1987, 2000). Within couples, the behavior of partners was very similar. Compared to military couples without PTSD, couples with PTSD displayed more interpersonal hostility and control. Couples with PTSD also exhibited more sulking, blaming, and controlling behavior, and less affirming and connecting behavior, than couples without PTSD. Results advance our understanding of the relational impacts of PTSD on military service members and their partners, and underscore the value of couple-based interventions for PTSD in the context of relationship distress