Role of the micro/macro structure of welds in crack nucleation and propagation in aerospace aluminum-lithium alloy

Al-Li alloys offer the benefits of increased strength, elastic modulus and lower densities as compared to conventional aluminum alloys. Martin Marietta Laboratories has developed an Al-Li alloy designated 2195 which is designated for use in the cryogenic tanks of the space shuttle. The Variable Polarity Plasma Arc (VPPA) welding process is currently being used to produce these welds [1]. VPPA welding utilizes high temperature ionized gas (plasma) to transfer heat to the workpiece. An inert gas, such as Helium, is used to shield the active welding zone to prevent contamination of the molten base metal with surrounding reactive atmospheric gases. [1] In the Space Shuttle application, two passes of the arc are used to complete a butt-type weld. The pressure of the plasma stream is increased during the first pass to force the arc entirely through the material, a practice commonly referred to as keyholing. Molten metal forms on either side of the arc and surface tension draws this liquid together as the arc passes. 2319 Al alloy filler material may also be fed into the weld zone during this pass. During the second pass, the plasma stream pressure is reduced such that only partial penetration of the base material is obtained. Al 2319 filler material is added during this pass to yield a uniform, fully filled welded joint. This additional pass also acts to alter the grain structure of the weld zone to yield a higher strength joint

Modeling beta decay spectra to analyze the sensitivity of a neutrino mass experiment

Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2018.Cataloged from PDF version of thesis.Includes bibliographical references (pages 46-47).The Project 8 experiment aims to measure the electron neutrino mass by obtaining and analyzing [beta] spectra from tritium decay. Using an inferential model of the experiment's anticipated data, I evaluate its projected sensitivity to certain parameters of interest. I focus on the precision and accuracy with which Project 8 can expect to resolve the [beta]-decay spectrum's endpoint in an upcoming stage of the experiment. I also present an initial prediction of Project 8's eventual expected sensitivity to the electron neutrino mass. This analysis involved generating and analyzing [beta]-decay spectral data using a model implemented in Stan, a platform for Bayesian statistical inference. The sensitivity analysis was designed to account for the anticipated distribution of results (mass and endpoint measurements) produced by the potential variation in a number of physical and experimental parameters. In addition, the method used here allows for a calibration of the consequences of inferences and decisions made in reaching those results. I find that, using one year of Project 8 Phase II data, the T2 endpoint can be resolved within a 13.7 eV window (90% C.I.) with 62% coverage (or accuracy), corresponding to a 4.1 eV posterior standard deviation. Preliminarily, using one year of Phase IV data, the electron neutrino mass can be resolved within a 0.051 eV window (90% C.I.) with 56% coverage. I also outline a way that model-based sensitivity procedures and calibration of inference can be extended to the neutrino mass hierarchy problem.by Talia E. Weiss.S.B

What Does the Current Research Say About Effective Strategies for Teaching Reading Fluency?

Reading fluency, a person’s ability to read with speed, accuracy, and prosody, is one of the five major dimensions of reading instruction. Effective reading fluency instruction is crucial to the success of developing readers. The ability to read fluently directly impacts the ability to engage in other reading skills, as instruction with reading fluency is often integrated with skills such as reading comprehension and phonics. There are a plethora of evidence-based strategies for teaching reading instruction. While these strategies vary the delivery of instruction or materials needed, they all share a foundation of thorough research and continued efficacy in the field of education. In order to maximize the potential for student success in reading fluency and reading ability overall, the employment of some of these evidence-based strategies is essential and noteworthy for educators. The following is a literature review detailing what the current research suggests for effective instruction in reading fluency

Microstructural analysis of the 2195 aluminum-lithium alloy welds

The principal objective of this research was to explain a tendency of 2195 Al-Li alloy to crack at elevated temperature during welding. Therefore, a study was made on the effect of welding and thermal treatment on the microstructure of Al-Li Alloy 2195. The critical roles of precipitates, boundaries, phases, and other features of the microstructure were inferred from the crack propagation paths and the morphology of fracture surface of the alloy with different microstructures. Particular emphasis was placed on the microstructures generated by the welding process and the mechanisms of crack propagation in such structures. Variation of the welding parameters and thermal treatments were used to alter the micro/macro structures, and they were characterized by optical and scanning electron microscopy. A theoretical model is proposed to explain changes in the microstructure of welded material. This model proposes a chemical reaction in which gases from the air (i.e., nitrogen) release hydrogen inside the alloy. Such a reaction could generate large internal stresses capable to induce porosity and crack-like delamination in the material

Microstructural analysis of cracks generated during welding of 2195 aluminum-lithium alloy

This research summarizes a series of studies conducted at Marshall Space Flight Center to characterize the properties of 2195 Al-Li alloy. 2195 Al-Li alloy, developed by Martin Marietta laboratories, is designated as a replacement of 2219 Al-Cu alloy for the External Tank (E.T.) of the space shuttle. 2195 Al-Li alloy with its advantage of increased strength per weight over its predecessor, 2219 Al-Cu alloy, also challenges current technology. 2195 Al-Li has a greater tendency to crack than its predecessor. The present study began with the observation of pore formation in 2195 Al-Li alloy in a thermal aging process. In preliminary studies, Talia and Nunes found that most of the two pass welds studied exhibited round and crack-like porosity at the weld roots. Furthermore, the porosity observed was associated with the grain boundaries. The porosity level can be increased by thermal treatment in the air. A solid state reaction proceeding from dendritic boundaries in the weld fusion zone was observed to correlate with the generation of the porosity

Fiduciary Law in Financial Regulation

This chapter explores the application of fiduciary duties to regulated financial firms and financial services. At first blush, the need for such a chapter might strike some as surprising in that fiduciary duties and systems of financial regulation can be conceptualized as governing distinctive and nonoverlapping spheres: fiduciary duties police private activity through open-ended, judicially defined standards imposed on an ex post basis, whereas financial regulations set largely mandatory, ex ante obligations for regulated entities under supervisory systems established in legislation and implemented through expert administrative agencies. Yet, as the chapter documents, fiduciary duties often do overlap with systems of financial regulation. In many regulatory contexts, fiduciary duties arise as a complement to, or sometimes substitute for, other mechanisms of financial regulation. Moreover, the interactions between fiduciary duties and systems of financial regulation generate a host of recurring and challenging interpretative issues. The chapter explores the reasons fiduciary duties arise so frequently in the field of financial regulation and provides a structured account of how the principles of fiduciary duties interact with the more rule-based legal requirements that characterize financial regulation. As grist for this undertaking the chapter focuses on a set of roughly two dozen judicial decisions and administrative rulings to illustrate its claims

AGN feedback at z~2 and the mutual evolution of active and inactive galaxies

The relationships between galaxies of intermediate stellar mass and moderate luminosity active galactic nuclei (AGNs) at 1<z<3 are investigated with the Galaxy Mass Assembly ultra-deep Spectroscopic Survey (GMASS) sample complemented with public data in the GOODS-South field. Using X-ray data, hidden AGNs are identified in unsuspected star-forming galaxies with no apparent signs of non-stellar activity. In the color-mass plane, two parallel trends emerge during the ~2 Gyr between the average redshifts z~2.2 and z~1.3: while the red sequence becomes significantly more populated by ellipticals, the majority of AGNs with L(2-10 keV)>10^42.3 erg s^-1 disappear from the blue cloud/green valley where they were hosted predominantly by star-forming systems with disk and irregular morphologies. These results are even clearer when the rest-frame colors are corrected for dust reddening. At z~2.2, the ultraviolet spectra of active galaxies (including two Type 1 AGNs) show possible gas outflows with velocities up to about -500 km s^-1 that are not observed neither in inactive systems at the same redshift, nor at lower redshifts. Such outflows indicate the presence of gas that can move faster than the escape velocities of active galaxies. These results suggest that feedback from moderately luminous AGNs (logL_X~2 by contributing to outflows capable of ejecting part of the interstellar medium and leading to a rapid decrease in the star formation in host galaxies with stellar masses 10<logM<11 M_Sun.Comment: Astrophysical Journal Letters, in press (6 pages, 4 figures

The star formation rate cookbook at 1 < z < 3: Extinction-corrected relations for UV & [OII]{\lambda}3727 luminosities

We use a spectroscopic sample of 286 star-forming galaxies (SFGs) at 1<z<3 from the GMASS survey to study different star formation rate (SFR) estimators. Infrared (IR) data are used to derive empirical calibrations to correct ultraviolet (UV) and [OII]{\lambda}3727 luminosities for dust extinction and dust-corrected estimates of SFR. In the selection procedure we fully exploit the available spectroscopic information. On the basis of three continuum indices, we are able to identify and exclude from the sample galaxies in which old stellar populations might bring a non-negligible contribution to IR luminosity (LIR) and continuum reddening. Using Spitzer-MIPS and Herschel-PACS data we derive LIR for two-thirds of our sample. The LIR/LUV ratio is used as a probe of effective attenuation (AIRX) to search for correlations with continuum and spectroscopic features. The relation between AIRX and UV continuum slope ({\beta}) was tested for our sample and found to be broadly consistent with the literature results at the same redshift, though with a larger dispersion with respect to UV-selected samples. We find a correlation between the rest-frame equivalent width (EW) of the [OII]{\lambda}3727 line and {\beta}, which is the main result of this work. We therefore propose the [OII]{\lambda}3727 line EW as a dust attenuation probe and calibrate it through AIRX, though the assumption of a reddening curve is still needed to derive the actual attenuation towards the [OII]{\lambda}3727 line. We tested the issue of differential attenuation towards stellar continuum and nebular emission: our results are in line with the traditional prescription of extra attenuation towards nebular lines. A set of relations is provided that allows the recovery of the total unattenuated SFR from UV and [OII]{\lambda}3727 luminosities. (Abridged)Comment: Accepted for publication in A&A; 20 pages, 19 figures, 5 table

Service Quality Agriculture Counseling and Satisfaction Farmers in Farming Development (Case Study on VegetableiFarmers in Nania Village, Baguala District, Ambon City)

Development goals in Indonesia have existed for a long time, with the main objective of prioritizing the agricultural sector and increasing agricultural welfare. Through extension activities which are a series of ongoing processes according to the needs of farmers. The presence of agricultural extension workers as the spearhead of implementing agricultural development. Improving the performance of agricultural extension agents also determines future agricultural development, which determines the income of the agricultural sector. Good service quality is a determinant of the success of agricultural development. This study aimed to assess the quality of agricultural extension services and farmers' satisfaction level in developing vegetable farming in Nania Village. This research was conducted in Nania Village from November 2022 to December 2022. The type of research used was census research. The total population in this study was 16 people, all of whom were vegetable farmers in the village of Nania. The sample in this study was the entire population. The type of data collected includes primary data and secondary data. The data analysis technique used is descriptive qualitative data analysis. The results showed that the quality of counseling services on indicators of counseling preparation was in the medium category with an average (2.30), the implementation of counseling was in the medium category (2.15), and the appropriateness of the counseling method (2.49) was in the high category. While the level of farmer satisfaction with agricultural extension services, seen from the accuracy of the service, is classified as medium (2.2), and the performance of extension workers are classified as high or very good with an average (2.65). The conclusion is that the quality of agricultural extension services in Nania Village is in the moderate or adequate category. And the level of farmer satisfaction with extension services is classified as medium and high categories

Low-Calorie Sweetened Beverage Consumption Does Not Reduce Total Energy or Sugar Intake among Children

Beverages containing low-calories sweeteners (LCSB) are used as alternatives to sugar-sweetened beverages (SSBs), yet their effects on the overall diet and effectiveness for weight management are unclear. The objective of this analysis was to examine energy and macronutrient intake among children who report LCSB and SSB consumption. The findings of this analysis challenge the utility of LCSB consumption as a strategy for weight management in children