The Rossiter equation: Improving the fractional vortex speed and defining an effective length to depth ratio for cavity flows.

This paper first reviews well known analytical techniques for predicting the Rossiter modes of a cavity in compressible flow. We combine existing methods to improve the performance in compressible flow. Second, we introduce a method based on an effective length to depth ratio of the cavity from experimental results for predicting frequencies across Mach numbers. Finally, the fractional vortex speed used in the Rossiter equation and its derivatives is calculated from high subsonic (M 0.55) to supersonic (M 2.3) for use in future cavity mode prediction.

Remuneration and Recruitment of Study Participants for AD Cohort Studies From the General Public and From Minority Communities.

INTRODUCTION: Offering remuneration for participation in studies of aging and Alzheimer Disease (AD) may improve recruitment, particularly among minoritized and low-income groups. But remuneration may also raise ethical problems and reduce altruistic motivations for participation. METHODS: A nationally representative sample of Americans (N=2030) with large (N=500) Black and Hispanic oversamples was asked about willingness to participate in a longitudinal AD cohort study after random assignment of remuneration ($0, $50/visit, $100/visit). Respondents were then asked about their perceived burden, risks, and societal contribution from participation. RESULTS: An offer of remuneration increased willingness to participate, with no difference between $50 and $100. The increase was similar across racial, ethnic, and income groups. Remuneration did not affect perceived risks or altruistic benefits. Compensation caused Whites and Hispanics, but not Blacks, to lower the perceived burden. DISCUSSION: Modest levels of remuneration are likely to improve recruitment to AD research studies without causing collateral ethical or motivation problems. Remuneration does not differentially enhance minority recruitment.

Retention of Study Partners in Longitudinal Studies of Alzheimer Disease.

BACKGROUND: Study partners are required for all participants at Alzheimer's Disease Research Centers (ADRCs). Study partners' attitudes and beliefs may contribute to missed visits and negatively impact retention of participants in longitudinal AD studies. OBJECTIVE: Study partners (N = 212) of participants (Clinical Dementia Rating® [CDR]≤2) at four ADRCs were randomly surveyed to examine their facilitators and barriers to continued participation in AD studies. METHODS: Reasons for participation were analyzed with factor analysis and regression analysis. Effects of complaints and goal fulfillment on attendance were estimated with fractional logistic models. Open-ended responses were characterized with a Latent Dirichlet Allocation topic model. RESULTS: Study partners participated for personal benefit and altruism. They emphasized personal benefits more when their participants had a CDR > 0 than when they had a CDR = 0. This difference declined with participant age. The majority of study partners rated their ADRC participation as positive and meeting their goals. Although half reported at least one complaint, very few regretted participating. Those who reported that ADRC participation fulfilled their goals or had fewer complaints were more likely to have perfect attendance. Study partners requested more feedback about test results and better management of study visits. CONCLUSION: Study partners are motivated by both personal and altruistic goals. The salience of each goal depends on their trust in researchers and the participant's cognitive status and age. Retention may improve with perceived goal fulfillment and fewer complaints. Potential areas for improving retention are providing more information about the participant's test results and better management of study visits.

Psychometric Evaluation of the Perceived Research Burden Assessment (PeRBA) in Longitudinal Studies of Alzheimer Disease Using Rasch Analysis.

INTRODUCTION: The Perceived Research Burden Assessment (PeRBA) was developed to measure participant perceptions of burden in research studies. This study aimed to examine the psychometric properties of this assessment using Rasch analysis in participants in the longitudinal studies of the Alzheimer disease (AD) and their family members. METHODS: PeRBA was administered to 443 participants in studies of AD and 212 family members across 4 Alzheimer Disease Research Centers. We used Rasch analysis to examine PeRBA's psychometric properties, and data-model fit both at item and scale levels. RESULTS: PeRBA demonstrated good reliability and item and person fit for participants and family members. A few items did not fit the model for participants or family members. Areas of content redundancy were found in items assessing similar amounts of perceived research burden. Areas of content gaps were also found, with no items assessing certain levels of perceived research burden. CONCLUSION: Analysis results support the good overall psychometric properties of PeRBA among research participants in studies of AD and their family members. Recommendations have been provided to improve the assessment, including rewording items and adding items that could account for a broader range of perceived research burden.

Perceptions of Research Burden and Retention Among Participants in ADRC Cohorts.

OBJECTIVES: Alzheimer disease (AD) and related dementias clinical research is associated with significant participant burden. The Perceived Research Burden Assessment (PeRBA) measures participants' perceptions of logistical, psychological, and physical burdens. The purpose of this study was to assess PeRBA's psychometric properties, perceptual sources, and behavioral consequences with participants in a multisite study of participant retention in longitudinal cohort studies of Alzheimer disease and related dementias. DESIGN: Multicenter mixed methods. SETTING: In-person or phone. PARTICIPANTS: A total of 443 participants at 4 NIA-funded Alzheimer Disease Research Centers (ADRCs) were randomly selected and invited to participate if they were 45 years of age or more, enrolled in longitudinal studies, and had a Clinical Dementia Rating Scale global score ≤1. MEASUREMENTS: Participants completed a 20-minute survey including the 21-item PeRBA about their research participation. RESULTS: PeRBA demonstrated high-internal consistency and convergent validity. PeRBA scores correlated with expected perceptual factors. Higher PeRBA scores were associated with lower attendance and higher dropout rates. CONCLUSIONS: PeRBA can be used by researchers to identify participants who may feel overburdened and tailor approaches and strategies to support participants in longitudinal AD studies, maximizing participation, and reducing dropout. Making efforts to increase participants' understanding of study procedures, and building and maintaining trust throughout the study, can contribute to reducing perceived burden and potentially increasing retention in longitudinal AD studies.

Retaining Participants in Longitudinal Studies of Alzheimer's Disease.

BACKGROUND: Retention of study participants is essential to advancing Alzheimer's disease (AD) research and developing therapeutic interventions. However, recent multi-year AD studies have lost 10% to 54% of participants. OBJECTIVE: We surveyed a random sample of 443 participants (Clinical Dementia Rating [CDR]≤1) at four Alzheimer Disease Research Centers to elucidate perceived facilitators and barriers to continued participation in longitudinal AD research. METHODS: Reasons for participation were characterized with factor analysis. Effects of perceived fulfillment of one's own goals and complaints on attendance and likelihood of dropout were estimated with logistic regression models. Open-ended responses suggesting study improvements were analyzed with a Latent Dirichlet Allocation topic model. RESULTS: Factor analyses revealed two categories, personal benefit and altruism, as drivers of continued participation. Participants with cognitive impairment (CDR > 0) emphasized personal benefits more than societal benefits. Participants with higher trust in medical researchers were more likely to emphasize broader social benefits. A minority endorsed any complaints. Higher perceived fulfillment of one's own goals and fewer complaints were related to higher attendance and lower likelihood of dropout. Facilitators included access to medical center support and/or future treatment, learning about AD and memory concerns, and enjoying time with staff. Participants' suggestions emphasized more feedback about individual test results and AD research. CONCLUSION: The results confirmed previously identified facilitators and barriers. Two new areas, improved communication about individual test results and greater feedback about AD research, emerged as the primary factors to improve participation.

Imaging Charged Exciton Localization in van der Waals WSe2/MoSe2 Heterobilayers.

Exciton localization in transition-metal dichalcogenide monolayers is behind a variety of interesting phenomena and applications, including broad-spectrum solar cells and single-photon emissions. Strain fields at the periphery of topographically distinct features such as nanoscopic bubbles were recently associated with localized charge-neutral excitons. Here, we use tip-enhanced photoluminescence (PL) to visualize excitons in WSe2/MoSe2 heterobilayers (HBL). We find strong optical emission from charged excitons, particularly positively charged trions, in HBL supported by interlayer charge transfer. Our results reveal strong trion confinement, with a localization length scale comparable to the trion size, at the apex region inside individual nanoscopic bubbles. Nano-PL mapping also shows sub-10-nm spatial variations in the localized trion emission spectra, which stem from atomic-scale potential energy fluctuations. These findings demonstrate the possibility of confining charged exciton complexes that are electrically tunable, opening up further opportunities to probe many-body exciton physics and to explore additional possible sites for strong exciton localization that can lead to quantum emission.

Mapping Molecular Adsorption Configurations with <5 nm Spatial Resolution through Ambient Tip-Enhanced Raman Imaging.

We interrogate para-mercaptobenzoic acid (MBA) molecules chemisorbed onto plasmonic silver nanocubes through tip-enhanced Raman (TER) spectral nanoimaging. Through a detailed examination of the spectra, aided by correlation analysis and density functional theory calculations, we find that MBA chemisorbs onto the plasmonic particles with at least two distinct configurations: S- and CO2-bound. High spatial resolution TER mapping allows us to distinguish between the distinct adsorption geometries with a pixel-limited (<5 nm) spatial resolution under ambient laboratory conditions.

The ideological divide in confidence in science and participation in medical research.

In the United States, the wide ideological divergence in public confidence in science poses a potentially significant problem for the scientific enterprise. We examine the behavioral consequences of this ideological divide for Americans' contributions to medical research. Based on a mass survey of American adults, we find that engagement in a wide range of medical research activities is a function of a latent propensity to participate. The propensity is systematically higher among liberals than among conservatives. A substantial part of this ideological divide is due to conservative Americans' lower confidence in science. These findings raise important issues for the recruitment of subjects for medical studies and the generalizability of results from such studies.

Political Ideology, Confidence in Science, and Participation in Alzheimer Disease Research Studies.

BACKGROUND: Americans' confidence in science varies based on their political ideology. This ideological divide has potentially important effects on citizens' engagement with and participation in clinical studies of Alzheimer disease (AD). METHODS: A probability sample of 1583 Americans was surveyed about their willingness to participate in longitudinal AD research and about their political attitudes. These survey results were compared with a survey of 382 participants in a longitudinal AD study at the Knight Alzheimer Disease Research Center. RESULTS: Among Americans, more conservative ideology decreases willingness to participate in a hypothetical longitudinal cohort study of AD both directly and through its negative effect on confidence in science. The Knight Alzheimer Disease Research Center study participants expressed more liberal ideology and greater confidence in science than Americans in general. Of the survey respondents opposed to participation, over a quarter changed to neutral or positive if the study returned their research results to them. CONCLUSIONS AND RELEVANCE: Clinical studies of AD are likely biased toward participants who are more liberal and have higher confidence in science than the general population. This recruitment bias may be reduced by lowering the trust demanded of participants through measures such as returning research results to participants.

Attitudes of Research Participants and the General Public Regarding Disclosure of Alzheimer Disease Research Results.

IMPORTANCE: Results of Alzheimer disease (AD) research assessments typically are not disclosed to participants. Recent research has suggested interest in disclosure, but, to our knowledge, few studies have accounted for awareness of potential benefits and limitations of disclosure. OBJECTIVE: To determine the attitudes of cognitively normal research participants and members of the general public regarding disclosure of AD research results. DESIGN, SETTING, AND PARTICIPANTS: Participants in a longitudinal aging study (Alzheimer Disease Research Center [ADRC]) were given preintervention and postintervention surveys about disclosure attitudes. In a general public sample (The American Panel Survey), participants responded to a similar survey about disclosure attitudes. INTERVENTIONS: Participants in the ADRC sample were randomly assigned to a group (n = 119) that read an education intervention about the usefulness of AD biomarkers or to a placebo group (n = 100) that read as its intervention general information about the ADRC. Participants in the general public sample read a brief vignette describing participation in a longitudinal AD study. MAIN OUTCOME AND MEASURE: Interest in disclosure of AD research results. RESULTS: Cognitively normal ADRC participants (n = 219) were 60.7% (n = 133) female, 83.6% (n = 183) of white race, and reported a mean of 15.91 years of education. Twenty-nine individuals refused participation. The American Panel Survey participants (n = 1418) indicated they did not have AD and were 50.5% (n = 716) female, 76.7% (n = 1087) of white race, and reported a mean of 13.85 years of education. Overall, 77.6% of eligible participants (1583 of 2041) completed the survey in July 2014. Interest in disclosure was high among the ADRC participants (55.1% [119 of 216] were "extremely interested"). Viewing the education intervention predicted lower interest in disclosure (odds ratio, 2.01; 95% CI, 1.15-3.53; P = .02). High subjective risk of AD, a family history of AD, and minimal attendance at research meetings were associated with high interest after the intervention. In the general public, interest was lower overall (12.5% [174 of 1389] were "extremely interested"), but the subset of participants most likely to join an AD research study reported higher interest (43.5% [40 of 92] were extremely interested). CONCLUSIONS AND RELEVANCE: Experience with AD appears to increase interest in disclosure of AD research results. Learning about potential limitations of disclosure somewhat tempered interest. These findings should inform the development of disclosure policies for asymptomatic individuals in AD studies.

Temporoparietal hypometabolism in frontotemporal lobar degeneration and associated imaging diagnostic errors.

OBJECTIVE: To evaluate the cause of diagnostic errors in the visual interpretation of positron emission tomographic scans with fludeoxyglucose F 18 (FDG-PET) in patients with frontotemporal lobar degeneration (FTLD) and patients with Alzheimer disease (AD). DESIGN: Twelve trained raters unaware of clinical and autopsy information independently reviewed FDG-PET scans and provided their diagnostic impression and confidence of either FTLD or AD. Six of these raters also recorded whether metabolism appeared normal or abnormal in 5 predefined brain regions in each hemisphere-frontal cortex, anterior cingulate cortex, anterior temporal cortex, temporoparietal cortex, and posterior cingulate cortex. Results were compared with neuropathological diagnoses. SETTING: Academic medical centers. PATIENTS: Forty-five patients with pathologically confirmed FTLD (n=14) or AD (n=31). RESULTS: Raters had a high degree of diagnostic accuracy in the interpretation of FDG-PET scans; however, raters consistently found some scans more difficult to interpret than others. Unanimity of diagnosis among the raters was more frequent in patients with AD (27 of 31 patients [87%]) than in patients with FTLD (7 of 14 patients [50%]) (P=.02). Disagreements in interpretation of scans in patients with FTLD largely occurred when there was temporoparietal hypometabolism, which was present in 7 of the 14 FTLD scans and 6 of the 7 scans lacking unanimity. Hypometabolism of anterior cingulate and anterior temporal regions had higher specificities and positive likelihood ratios for FTLD than temporoparietal hypometabolism had for AD. CONCLUSIONS: Temporoparietal hypometabolism in FTLD is common and may cause inaccurate interpretation of FDG-PET scans. An interpretation paradigm that focuses on the absence of hypometabolism in regions typically affected in AD before considering FTLD is likely to misclassify a significant portion of FTLD scans. Anterior cingulate and/or anterior temporal hypometabolism indicates a high likelihood of FTLD, even when temporoparietal hypometabolism is present. Ultimately, the accurate interpretation of FDG-PET scans in patients with dementia cannot rest on the presence or absence of a single region of hypometabolism but rather must take into account the relative hypometabolism of all brain regions.

Validation of consensus panel diagnosis in dementia.

BACKGROUND: The clinical diagnosis of dementing diseases largely depends on the subjective interpretation of patient symptoms. Consensus panels are frequently used in research to determine diagnoses when definitive pathologic findings are unavailable. Nevertheless, research on group decision making indicates that many factors can adversely affect panel performance. OBJECTIVE: To determine conditions that improve consensus panel diagnosis. DESIGN: Comparison of neuropathologic diagnoses with individual and consensus panel diagnoses based on clinical scenarios only, fludeoxyglucose F 18 positron emission tomography images only, and scenarios plus images. SETTING: Expert and trainee individual and consensus panel deliberations using a modified Delphi method in a pilot research study of the diagnostic utility of fludeoxyglucose F 18 positron emission tomography. PATIENTS: Forty-five patients with pathologically confirmed Alzheimer disease or frontotemporal dementia. MAIN OUTCOME MEASURES: Statistical measures of diagnostic accuracy, agreement, and confidence for individual raters and panelists before and after consensus deliberations. RESULTS: The consensus protocol using trainees and experts surpassed the accuracy of individual expert diagnoses when clinical information elicited diverse judgments. In these situations, consensus was 3.5 times more likely to produce positive rather than negative changes in the accuracy and diagnostic certainty of individual panelists. A rule that forced group consensus was at least as accurate as majority and unanimity rules. CONCLUSIONS: Using a modified Delphi protocol to arrive at a consensus diagnosis is a reasonable substitute for pathologic information. This protocol improves diagnostic accuracy and certainty when panelist judgments differ and is easily adapted to other research and clinical settings while avoiding the potential pitfalls of group decision making.

A social choice approach to expert consensus panels.

This study uses recent theoretical work about group decision-making to assess the quality of decision-making by expert consensus panels. We specifically examine (1) when individual members of panels will divulge their private judgments about the decision to the panel, and (2) when the group judgment is superior to the judgment of individual panelists and will lead to better treatment for patients. We conclude that to maximize the chance of an accurate decision, panels should be made as large as possible, adopt the smallest supermajority rule, and attract members with the highest individual competencies. Furthermore, interdependence among panelists and the goal of reaching consensus can reduce the efficacy of these panels.