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Nanoscale heterogeneity (including size, shape, strain, and defects) significantly impacts material properties and how they function. Bragg coherent x-ray imaging methods have emerged as a powerful tool to investigate, in three-dimensional detail, the local material response to external stimuli in reactive environments, thereby enabling explorations of the structure-defect-function relationship at the nanoscale. Although progress has been made in understanding this relationship, coherent imaging of extended samples is relatively slow (typically requiring many minutes) due to the experimental constraints required to solve the phase problem. Here, we develop Bragg coherent modulation imaging (BCMI), which uses a modulator to solve the phase problem thereby enabling fast, local imaging of an extended sample. Because a known modulator is essential to the technique, we first demonstrate experimentally that an unknown modulator structure can be recovered by using the exit wave diversity that exists in a standard Bragg coherent diffraction imaging (BCDI) experiment. We then show with simulations that a known modulator constraint is sufficient to solve the phase problem and enable a single view of an extended sample that is sensitive to defects and dislocations. Our results pave the way for BCMI investigations of strain and defect dynamics in complex extended crystals with temporal resolution limited by the exposure time of a single diffraction pattern.

Defects and their interactions in crystalline solids often underpin material properties and functionality as they are decisive for stability, result in enhanced diffusion, and act as a reservoir of vacancies. Recently, lithium-rich layered oxides have emerged among the leading candidates for the next-generation energy storage cathode material, delivering 50 % excess capacity over commercially used compounds. Oxygen-redox reactions are believed to be responsible for the excess capacity, however, voltage fading has prevented commercialization of these new materials. Despite extensive research the understanding of the mechanisms underpinning oxygen-redox reactions and voltage fade remain incomplete. Here, using operando three-dimensional Bragg coherent diffractive imaging, we directly observe nucleation of a mobile dislocation network in nanoparticles of lithium-rich layered oxide material. Surprisingly, we find that dislocations form more readily in the lithium-rich layered oxide material as compared with a conventional layered oxide material, suggesting a link between the defects and the anomalously high capacity in lithium-rich layered oxides. The formation of a network of partial dislocations dramatically alters the local lithium environment and contributes to the voltage fade. Based on our findings we design and demonstrate a method to recover the original high voltage functionality. Our findings reveal that the voltage fade in lithium-rich layered oxides is reversible and call for new paradigms for improved design of oxygen-redox active materials.

Surface chemistry is important across diverse fields such as corrosion and nanostructure synthesis. Unfortunately, many as-synthesized nanomaterials, including partially dealloyed nanoparticle catalysts for fuel cells, with highly active surfaces are not stable in their reactive environments, preventing widespread application. Thus, understanding instability by focusing on the structure-stability and defect-stability relationship at the nanoscale is crucial and will likely play an important role in meeting grand challenges. To this end, recent advances in imaging nanostructure stability have come via both electron, x-ray, and other techniques such as atomic force microscopy, but tend to be limited to specific sample environments and/or two-dimensional images. Here, we report investigations into the defect-stability relationship of silver nanoparticles to voltage-induced electrochemical dissolution imaged in-situ in three-dimensional (3D) detail by Bragg Coherent Diffractive Imaging (BCDI). We first determine the average dissolution kinetics by Stationary Probe Rotating Disk Electrode (SPRDE) in combination with inductively coupled plasma mass spectrometry (ICP-MS), which allows real-time in-situ measurement of Ag+ ions formation and the corresponding electrochemical current. We then observe the dissolution and redeposition processes in 3D with BCDI in single nanocrystals, providing unique insight about the role of surface strain, defects, and their coupling to the dissolution chemistry. The methods developed and the knowledge gained go well beyond a "simple" silver electrochemistry and are applicable to all electrocatalytic reactions where functional links between activity and stability are controlled by structure and defect dynamics., Comment: 15 pages, 5 figures

Longitudinal data on the academic performance of high school and college students who completed the ACT Assessment Program beginning in 1964-5 are reported. Specifically, trends in students' high school averages, their test scores on the ACT, and their first semester college grade point averages are examined. Over an eight year period, grades awarded by high school and college faculty have shown a significant increase while at the same time ACT test scores have been on the decline. The results are consistent across all types of institutions, and for various subgroups of students. (Author)

Data reported in this paper are drawn from The American College Testing Program (ACT) files of student records collected over the five year period from 1970-71 to 1974-75 through administration of the ACT Assessment Program. The data from 1970-71 and 1971-72 represent a five percent random sample and the data from 1972-73, 1973-74, and 1974-75, a ten percent random sample of students tested on the first four national test dates each year. Included in the students' records are their ACT test scores and self-reported high school grades, and their responses to the ACT Student Profile Section (SPS), which contains some 200 items about vocational plans, out-of-class high school accomplishments, educational needs, extracurricular plans, and general biographical information. All students who write the ACT Assessment complete the SPS. Three major categories of trend data based on ACT test scores and on selected elements from the SPS are reported in subsequent sections of this paper. These are trends in students' academic abilities, background characteristics (e.g., sex, race, and socioeconomic status), and educational plans and goals. Findings are summarized and some interpretations of their implications are offered. (Author/MV)

The validity of prediction equations based on American College Testing (ACT) Program test scores and high school grades is investigated. Presented are separate results for prediction equations based on ACT scores only, on high school grades only, and on both kinds of prediction jointly. Also included is a discussion of the relationship between equations and the length of time they have been in use. The study is based on data collected from a random sample of 260 colleges participating in the ACT Research Services from 1972-73 to 1976-77. The accuracy of prediction equations based on the two variables was found to be quite stable over time. A similar stability was noted in the accuracy of grade predictions for males and females separately. Grade predictions based on ACT scores only showed slightly greater stability over time than those based on grades only. It is concluded that despite the changes some colleges experience in student abilities, curricula, and grading practices over time, freshman grade averages can be accurately predicted using equations as old as four years. ACT policy is to update equations at least every three years. Data tables and statistical analyses are briefly discussed, and a brief list of references is included. (Author/MSE)

The validity of American College Testing (ACT) scores and self-reported high school grades in predicting college freshman grade average is documented, and the accuracy of prediction equations based on these measures is reported for institutions of differing freshman class size, affiliation, degree level, and racial/ethnic composition. Results are based on data collected from a random sample of 205 colleges that participated in the ACT Research Services in 1974-75 and 1976-77, with a separate prediction equation calculated for each college from its 1974-75 data. The predictive validity of ACT scores and high school grades was weakly related to freshman class size of more than 90. Prediction accuracy was moderately related to the institutional characteristics of affiliation, degree level, and racial/ethnic composition. Among the total college group, the accuracy of separate-sex predictions was less strongly related to freshman class size than to other institutional characteristics studied. However, it was more strongly related to freshman class size at private and four-year institutions than other kinds of institutions. Combined-sex equations based on simple random samples of size 50 from the base year data were almost as accurate as equations based on all records from the colleges, suggesting that ACT data could be used to make predictions of acceptable accuracy at colleges with as few as 50 freshmen. (Author/MSE)

Summarizes the data on math and science preparation and the results of the ACT Mathematics and Science Reasoning test for the nation's public high school graduating class of 1994. Highlights how the probability of student success in university science and math courses is affected. A rigorous high school program remains a significant precondition for success of both science and nonscience majors. (MLH)