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Diagnostic criteria for major depressive disorder allow for heterogeneous symptom profiles but genetic analysis of major depressive symptoms has the potential to identify clinical and etiological subtypes. There are several challenges to integrating symptom data from genetically informative cohorts, such as sample size differences between clinical and community cohorts and various patterns of missing data.
Methods
We conducted genome-wide association studies of major depressive symptoms in three cohorts that were enriched for participants with a diagnosis of depression (Psychiatric Genomics Consortium, Australian Genetics of Depression Study, Generation Scotland) and three community cohorts who were not recruited on the basis of diagnosis (Avon Longitudinal Study of Parents and Children, Estonian Biobank, and UK Biobank). We fit a series of confirmatory factor models with factors that accounted for how symptom data was sampled and then compared alternative models with different symptom factors.
Results
The best fitting model had a distinct factor for Appetite/Weight symptoms and an additional measurement factor that accounted for the skip-structure in community cohorts (use of Depression and Anhedonia as gating symptoms).
Conclusion
The results show the importance of assessing the directionality of symptoms (such as hypersomnia versus insomnia) and of accounting for study and measurement design when meta-analyzing genetic association data.
Depression is the largest global contributor to non-fatal disease burden(1). A growing body of evidence suggests that dietary behaviours, such as higher fruit and vegetable intake, may be protective against the risk of depression(2). However, this evidence is primarily from high-income countries, despite over 80% of the burden of depression being experienced in low- and middle-income countries(1). There are also limited studies to date focusing on older adults. The aim of this study was to prospectively examine the associations between baseline fruit and vegetable intake and incidence of depression in adults aged 45-years and older from 10 cohorts across six continents, including four cohorts from low and middle-income countries. The association between baseline fruit and vegetable intake and incident depression over a 3–6-year follow-up period was examined using Cox proportional hazard regression after controlling for a range of potential confounders. Participants were 7771 community-based adults aged 45+ years from 10 diverse cohorts. All cohorts were members of the Cohort Studies of Memory in an International Consortium collaboration(3). Fruit intake (excluding juice) and vegetable intake was collected using either a comprehensive food frequency questionnaire, short food questionnaire or diet history. Depressive symptoms were assessed using validated depression measures, and depression was defined as a score greater than or equal to a validated cut-off. Prior to analysis all data were harmonised. Analysis was performed by cohort and then cohort results were combined using meta-analysis. Subgroup analysis was performed by sex, age (45 – 64 versus 65+ years) and income level of country (high income countries versus low- and middle-income countries). There were 1537 incident cases of depression over 32,420 person-years of follow-up. Mean daily intakes of fruit were 1.7 ± 1.5 serves and vegetables 1.9 ± 1.4. serves. We found no association between fruit and vegetable intakes and risk of incident depression in any of the analyses, and this was consistent across the subgroup analyses. The low intake of fruit and vegetables of participants, diverse measures used across the different cohorts, and modest sample size of our study compared with prior studies in the literature, may have prevented an association being detected. Further investigation using standardised measures in larger cohorts of older adults from low- to middle-income countries is needed. Future research should consider the potential relationship between different types of fruits and vegetables and depression.
The accountability relationship between voters and elected members of Congress (MCs) hinges on the potential for citizens to learn about legislator behaviour. In an era of declining local newspapers, local television coverage of MCs potentially fulfils this important role. However, few studies have comprehensively examined the determinants of contemporary MC coverage by local television news broadcasts. In this paper, we leverage a vast database of local television news broadcast transcripts spanning two years to identify which factors explain MC coverage. We find that MCs receive little coverage outside the general election campaign season. Media market and campaign-specific factors are associated with more exposure when coverage occurs. Finally, we find that within competitive elections, incumbents receive only a marginal advantage in coverage. These findings provide a springboard to explore further questions regarding Congress, local media, and political accountability.
Pediatric cancer and cancer-related treatments may disrupt brain development and place survivors at risk for long term problems with cognitive functions. Processing efficiency has been operationalized as a nuanced cognitive skill that reflects both processing speed (PS) and working memory (WM) abilities and is sensitive to neurobiological disruption. Pediatric cancer survivors are at risk for processing efficiency deficits; however, a thorough characterization of processing efficiency skills across pediatric primary central nervous system (CNS) tumor and non-CNS cancer survivors has not yet been reported.
Participants and Methods:
Participants were selected from a mixed retrospective clinical database of pediatric cancer survivors (Total n=160; primary CNS tumor n=33; Non-CNS n=127). Univariate analyses were conducted to examine differences in processing efficiency mean scores (t-tests) and percent impairment (scores >1 SD below mean; chi-squared tests) between the total sample and normative sample, and across groups (CNS vs. Non-CNS). Multiple linear regressions were utilized to evaluate the relationships between additional risk factors, including biological sex, age at diagnosis, time since treatment, and socioeconomic status, and processing efficiency outcomes.
Results:
The total sample obtained lower scores on WM (M=90.83, SD=13.35) and PS (M=88.86, SD=14.38) measures than normative samples (M=100, SD=15), p < 0.001. Greater percentage of pediatric cancer survivors demonstrated impairment across all processing efficiency measures (24.8-38.1%) than normative samples (15.9%), p < 0.001. Regarding group differences, the CNS group obtained lower mean WM (M=84.85, SD =11.77) and PS (M=80, SD=14.18) scores than the Non-CNS group (WM M=92.39, SD=13.32; PS M=91.16, SD=13.56), p < 0.001. Rates of impairment between groups only differed for PS scores, with 63.6% of the CNS group and 31.5% of the non-CNS group demonstrating impairment, p < 0.001. Primary CNS tumor cancer type and male biological sex emerged as the only significant risk factors that predicted processing efficiency skills, with male sex predicting lower scores on PS (ß=8.91 p<.001) and semantic fluency (ß=7.59, p=.007).
Conclusions:
These findings indicate that both pediatric primary CNS tumor and non-CNS cancer survivors exhibit substantial weaknesses in processing efficiency skills after treatment. While both groups demonstrated deficits compared to normative samples, the CNS group was more susceptible to PS impairments than non-CNS group. A basic initial study of the relationships between risk factors and processing efficiency skills revealed that primary CNS cancer was a predictor of lower performance on working memory and processing speed measures, while male biological sex was a significant risk factor for worse performance on processing speed and semantic fluency measures. Continued focus on the construct of processing efficiency in pediatric cancer survivors is warranted. Applying a standardized approach to assessing and communicating this nuanced cognitive skill could contribute to advancing both clinical practice and outcomes research of pediatric cancer survivors.
Youth with sickle cell disease (SCD) are at increased risk of neurocognitive difficulties with and without neurological complications. Research has identified disease-related, socioeconomic, and sociodemographic risk factors as independently having significant associations with brain physiology for youth with SCD. Notably, sleep has a profound effect on youth’s neurocognitive abilities including learning, executive function, memory, attention, and processing speed. Furthermore, youth with SCD are at an increased risk for poor sleep measured by self-report questionnaires and by polysomnography (PSG). Within the SCD literature, only a few studies have examined the relationship between sleep and cognition. Of these, the majority examined individuals with SCD and comorbid sleep disorder diagnoses. The aim of this study is to identify associations between subjective sleep measures and neurocognitive outcomes in youth with SCD.
Participants and Methods:
This study investigated a cohort of 24 youth with SCD (ages 9-16, 11 males, 13 females; HbSS [63%], HbSB+ [8%], HbSC [21%], HbSB0 [8%]) who received sleep questionnaires and a neuropsychological evaluation. Exclusion criteria included a history of neurological disorder (e.g., overt stroke, seizures, or moyamoya disease) or prescribed psychotropic medication. Sleep questionnaires measuring sleep disturbance (e.g., sleep onset, sleep continuity, and sleep quality) and sleep-related impairments (e.g., daytime sleepiness, sleepiness interference with concentration, and difficulty with activities of daily living skills) were collected. Executive function, working memory, processing speed, and verbal comprehension measures were assessed. Demographics and disease-related risk factors were analyzed individually from medical records.
Results:
All analyses were controlled for age, the time between neuropsychological testing and sleep questionnaires, SCD genotype, and sex. Partial correlations were conducted to explore associations with neurocognitive outcomes. Verbal comprehension was significantly correlated with sleep disturbance (r= -.673, p=.001). Multiple linear regressions revealed that sleep disturbance significantly predicts verbal comprehension (ß= -.572, p=.003). Specifically, verbal comprehension decreased by 4.4 standard points for every one-point increase in sleep disturbance. Additionally, total sleep problems significantly predicted working memory (ß=-.414, p=.044) and processing speed (ß= -.411, p= .046). Specifically, working memory decreased by 3.5 standard points while processing speed decreased by 3.3 standard points for every one-point increase in total sleep problems reported. Sleep parameters did not significantly predict executive function.
Conclusions:
Results support the association between poor sleep and neurocognitive difficulty in youth with SCD. Three of the participants in this study received a PSG, which further demonstrates the importance of the current findings. This study serves to identify potential risk factors for neurocognitive deficits and provides potential methods for identifying youth with SCD who may need to be referred for a PSG assessment. Research should replicate these findings with increased sample sizes including utilizing PSG and investigating neurobiological effects. Findings may inform future screening tools, treatment approaches, and advanced cognitive initiatives and resources for this population.
Sleep has been shown to directly impact cognitive function throughout the lifespan; good quality sleep benefits and improves cognitive function, including processing speed and attention, while poor quality sleep can contribute to negative cognitive outcomes1. In particular, attention, learning, and memory have been demonstrated to be sensitive to sleeping changes, including fragmentation and restriction2. Subjective sleeping scales are utilized in both research and clinical practice, allowing sleep to be measured via self-report on various domains, including duration and factors that can contribute to sleep disruption and disturbances3. This study aims to examine the possible relation between subjective sleep quality and cognitive function among middle-aged adults to inform future research for early interventions of modifiable behaviors that can contribute to abnormal cognitive decline.
Participants and Methods:
Data for this analysis is part of the preliminary results of an ongoing pilot study. 29 middle-aged (40-65 years, inclusive), cognitively unimpaired individuals were recruited from the community. Subjective sleep quality was measured with the Pittsburgh Sleep Quality Index (PSQI). Attention and memory were measured using the California Verbal Learning Test, Third Edition (CVLT-III).
Results:
Multiple hierarchical regression analyses were conducted to evaluate if aspects of sleep quality were significantly correlated to complex attention and learning performance in this sample. First, correlation amylases showed significant relationships between PSQI Component 6 (Use of Sleeping Medication) and Trials 1 to 2 Learning Slope (R2 = -0.56, p =0.002) and CVLT-III Trials 1 through 5 Recall Discriminability (R2 = -0.42, p = 0.02), each with significant regression analyses outcomes (b =0.42, p = 0.04 and b = -0.46, p = 0.04, respectively). There were other variables that were found to be significantly correlated; however, after adjusting for relevant demographic variables (age, education, sex), the hierarchical regression analyses revealed no association between the aforementioned variables.
Conclusions:
While multiple aspects of sleep quality were expected to influence measures of attention and learning, only PSQI Component 6 was found to be statistically significantly associated with only two learning variables. Limitations of this study included a small sample size which was limited to cognitive and relatively physically healthy middle-aged adults. Further, sleep quality was measured with one subjective measure and no objective data was collected to support the hypotheses. Future analysis is needed to continue to explore the relation between subjective sleep quality and cognitive outcomes. As this is an ongoing study, we look forward to exploring this research question in more detail as the study progresses.
Policies that promote the common good may be politically infeasible if legislators representing ‘losing’ constituencies are punished for failing to promote their district's welfare. We investigate how varying the local and aggregate returns to a policy affects voter support for their incumbent. In our first study, we find that an incumbent who favours a welfare-enhancing policy enjoys a discontinuous jump in support when their district moves from losing to at least breaking even, while the additional incremental political returns for the district doing better than breaking even are modest. This feature of voter response, which we replicate, has significant implications for legislative politics generally and, in particular, how to construct politically feasible social welfare-enhancing policies. In a second study, we investigate the robustness of this finding in a competitive environment in which a challenger can call attention to a legislator's absolute and relative performance in delivering resources to their district.
As the scale of cosmological surveys increases, so does the complexity in the analyses. This complexity can often make it difficult to derive the underlying principles, necessitating statistically rigorous testing to ensure the results of an analysis are consistent and reasonable. This is particularly important in multi-probe cosmological analyses like those used in the Dark Energy Survey (DES) and the upcoming Legacy Survey of Space and Time, where accurate uncertainties are vital. In this paper, we present a statistically rigorous method to test the consistency of contours produced in these analyses and apply this method to the Pippin cosmological pipeline used for type Ia supernova cosmology with the DES. We make use of the Neyman construction, a frequentist methodology that leverages extensive simulations to calculate confidence intervals, to perform this consistency check. A true Neyman construction is too computationally expensive for supernova cosmology, so we develop a method for approximating a Neyman construction with far fewer simulations. We find that for a simulated dataset, the 68% contour reported by the Pippin pipeline and the 68% confidence region produced by our approximate Neyman construction differ by less than a percent near the input cosmology; however, they show more significant differences far from the input cosmology, with a maximal difference of 0.05 in $\Omega_{M}$ and 0.07 in w. This divergence is most impactful for analyses of cosmological tensions, but its impact is mitigated when combining supernovae with other cross-cutting cosmological probes, such as the cosmic microwave background.
A multisite research team proposed a survey to assess burnout among healthcare epidemiologists. Anonymous surveys were disseminated to eligible staff at SRN facilities. Half of the respondents were experiencing burnout. Staffing shortages were a key stressor. Allowing healthcare epidemiologists to provide guidance without directly enforcing policies may improve burnout.
Political divisions in the lead-up to the 2020 US presidential election were large, leading many to worry that heighted partisan conflict was so stark that partisans were living in different worlds, divided even in their understanding of basic facts. Moreover, the nationalization of American politics is thought to weaken attention to state political concerns. 2020 therefore provides an excellent, if difficult, test case for the claim that individuals understand their state political environment in a meaningful way. Were individuals able to look beyond national rhetoric and the national environment to understand state-level electoral dynamics? We present new data showing that, in the aggregate, despite partisan differences in electoral expectations, Americans are aware of their state's likely political outcome, including whether it will be close. At the same time, because forecasting the overall election outcome is more difficult, Electoral College forecasts are much noisier and display persistent partisan difference in expectations that do not differ much with state of residence.
Growing attitudinal and affective differences across party lines and increasing social polarization are often attributed to the strengthening of partisanship as a social identity. Scholars have paid less attention to personal preferences as a contributor to these phenomena. Our focus is on how citizens’ policy beliefs—their operational ideologies—are associated with their views of partisan groups. We examine our perspective with two studies. In the first, we find that the attribution of ideologically extreme political views to an individual's peer significantly reduces interest in interpersonal interaction but find limited evidence that partisan group membership alone induces social polarization. In the second, we show that citizens’ policy views are strongly associated with their perceptions of their own partisan group as well as their counterpartisans. Together, our results have important implications for understanding the consequences of increased polarization and partisan antipathy in contemporary politics.
Studies evaluating depression's role in lung cancer risk revealed contradictory findings, partly because of the small number of cases, short follow-up periods, and failure to account for key covariates including smoking exposure. We investigated the association of depressive symptoms with lung cancer risk in a large prospective cohort over 24 years while considering the role of smoking.
Methods
Women from the Nurses' Health Study completed measures of depressive symptoms, sociodemographics, and other factors including smoking in 1992 (N = 42 913). Depressive symptoms were also queried in 1996 and 2000, whereas regular antidepressant use and physician-diagnosed depression were collected starting in 1996. Multivariable Cox regression models estimated hazard ratios (HRs) and 95% confidence intervals (CIs) of lung cancer risk until 2016.
Results
We identified 1009 cases of lung cancer. Women with the highest v. lowest level of depressive symptoms had an increased lung cancer risk (HRsociodemographics-adjusted = 1.62, 95% CI 1.34–1.95; HRfully-adjusted = 1.25, 95% CI 1.04–1.51). In a test of mediation, lifetime pack-years of smoking accounted for 38% of the overall association between depressive symptoms and disease risk. When stratifying by smoking status, the elevated risk was evident among former smokers but not current or never smokers; however, the interaction term suggested no meaningful differences across groups (p = 0.29). Results were similar or stronger when considering time-updated depression status (using depressive symptoms, physician diagnosis, and regular antidepressant use) and chronicity of depressive symptoms.
Conclusions
These findings suggest that greater depressive symptoms may contribute to lung cancer incidence, directly and indirectly via smoking habits, which accounted for over a third of the association.
Whole-grain wheat, in particular coloured varieties, may have health benefits in adults with chronic metabolic disease risk factors. Twenty-nine overweight and obese adults with chronic inflammation (high-sensitivity C-reactive protein) > 1·0 mg/l) replaced four daily servings of refined grain food products with bran-enriched purple or regular whole-wheat convenience bars (approximately 41–45 g fibre, daily) for 8 weeks in a randomised, single-blind parallel-arm study where body weight was maintained. Anthropometrics, blood markers of inflammation, oxidative stress, and lipaemia and metabolites of anthocyanins and phenolic acids were compared at days 1, 29 and 57 using repeated-measures ANOVA within groups and ANCOVA between groups at day 57, with day 1 as a covariate. A significant reduction in IL-6 and increase in adiponectin were observed within the purple wheat (PW) group. TNF-α was lowered in both groups and ferulic acid concentration increased in the regular wheat (RW) group. Comparing between wheats, only plasma TNF-α and glucose differed significantly (P < 0·05), that is, TNF-α and glucose decreased with RW and PW, respectively. Consumption of PW or RW products showed potential to improve plasma markers of inflammation and oxidative stress in participants with evidence of chronic inflammation, with modest differences observed based on type of wheat.
Generative neural networks (GNNs) have successfully used human-created designs to generate novel 3D models that combine concepts from disparate known solutions, which is an important aspect of design exploration. GNNs automatically learn a parameterization (or latent space) of a design space, as opposed to alternative methods that manually define a parameterization. However, GNNs are typically not evaluated using an explicit notion of physical performance, which is a critical capability needed for design. This work bridges this gap by proposing a method to extract a set of functional designs from the latent space of a point cloud generating GNN, without sacrificing the aforementioned aspects of a GNN that are appealing for design exploration. We introduce a sparsity preserving cost function and initialization strategy for a genetic algorithm (GA) to optimize over the latent space of a point cloud generating autoencoder GNN. We examine two test cases, an example of generating ellipsoid point clouds subject to a simple performance criterion and a more complex example of extracting 3D designs with a low coefficient of drag. Our experiments show that the modified GA results in a diverse set of functionally superior designs while maintaining similarity to human-generated designs in the training data set.
The COllaborative project of Development of Anthropometrical measures in Twins (CODATwins) project is a large international collaborative effort to analyze individual-level phenotype data from twins in multiple cohorts from different environments. The main objective is to study factors that modify genetic and environmental variation of height, body mass index (BMI, kg/m2) and size at birth, and additionally to address other research questions such as long-term consequences of birth size. The project started in 2013 and is open to all twin projects in the world having height and weight measures on twins with information on zygosity. Thus far, 54 twin projects from 24 countries have provided individual-level data. The CODATwins database includes 489,981 twin individuals (228,635 complete twin pairs). Since many twin cohorts have collected longitudinal data, there is a total of 1,049,785 height and weight observations. For many cohorts, we also have information on birth weight and length, own smoking behavior and own or parental education. We found that the heritability estimates of height and BMI systematically changed from infancy to old age. Remarkably, only minor differences in the heritability estimates were found across cultural–geographic regions, measurement time and birth cohort for height and BMI. In addition to genetic epidemiological studies, we looked at associations of height and BMI with education, birth weight and smoking status. Within-family analyses examined differences within same-sex and opposite-sex dizygotic twins in birth size and later development. The CODATwins project demonstrates the feasibility and value of international collaboration to address gene-by-exposure interactions that require large sample sizes and address the effects of different exposures across time, geographical regions and socioeconomic status.
Objective: Radiation therapy (RT) improves rates of survival of patients with childhood brain tumors but increases deficits in cognition and independent living skills. Previous literature has studied difficulties in basic cognitive processes, but few explore impairment in higher-order skills such as adaptive functioning. Some studies identify females as at risk for cognitive deficits due to RT, but few investigate sex differences in adaptive functioning. It was hypothesized that females would exhibit poorer long-term independent living skills and core cognitive skills relative to males following RT. Methods: Forty-five adult survivors of posterior fossa childhood brain tumors (24 females) completed the Wechsler Abbreviated Scale of Intelligence (WASI-II), Wechsler Memory Scale, Third Edition (WMS-III) Digit Span Forward (DSF) and Backward (DSB), and Oral Symbol Digit Modalities Test (OSDMT). Informants completed the Scales of Independent Behavior-Revised (SIB-R). Results: DSF and OSDMT were positively correlated with all five SIB-R domains, full-scale IQ (FSIQ) was positively correlated with four SIB-R domains, and DSB was positively correlated with three SIB-R domains. There was an interaction between sex and RT for OSDMT and community living skills with trend level interactions for personal living skills and broad independent living skills, where females without RT had higher scores than females with RT. Conclusions: Female survivors were more affected by RT than males across the community living skills domain of adaptive functioning as well as processing speed. Processing speed deficits may have a cascading impact on daily living skills. Future studies should investigate how clinical and biological factors may contribute to personalized treatment plans between sexes. (JINS, 2019, 25, 729–739)
OBJECTIVES/SPECIFIC AIMS: The objective of this study is to use machine Learning techniques to generate maps of epithelium and lumen density in MRI space. METHODS/STUDY POPULATION: Methods: We prospectively recruited 39 patients undergoing prostatectomy for this institutional review board (IRB) approved study. Patients underwent MP-MRI before prostatectomy on a 3T field strength MRI scanner (General Electric, Waukesha, WI, USA) using an endorectal coil. MP-MRI included field-of-view optimized and constrained undistorted single shot (FOCUS) diffusion weighted imaging with 10 b-values (b=0, 10, 25, 50, 80, 100, 200, 500, 1000, and 2000), dynamic contrast enhanced imaging, and T2-weighted imaging. T2 weighted images were intensity normalized and apparent diffusion coefficient maps were calculated. The dynamic contrast enhanced data was used to calculate the percent change in signal intensity before and after contrast injection. All images were aligned to the T2 weighted image. Robotic prostatectomy was performed 2 weeks after image acquisition. Prostate samples were sliced using a 3D printed slicing jig matching the slice profile of the T2 weighted image. Whole mount samples at 10 μm thickness were taken, hematoxylin and eosin stained, digitized, and annotated by a board certified pathologist. A total of 210 slides were included in this study. Lumen and epithelium were automatically segmented using a custom algorithm written in MATLAB. The algorithm was validated by comparing manual to automatic segmentation on 18 samples. Slides were aligned with the T2 weighted image using a nonlinear control point warping technique. Lumen and epithelium density and the expert annotation were subsequently transformed into MRI space. Co-registration was validated by applying a known warp to tumor masks noted by the pathologist and control point warping the whole mount slide to match the transform. Overlap was measured using a DICE coefficient. A learning curve was generated to determine the optimal number of patients to train the algorithm on. A PLS algorithm was trained on 150 random permutations of patients incrementing from 1 to 29 patients. Slides were stratified such that all slides from a single patient were in the same cohort. Three cohorts were generated, with tumor burden balanced across all cohort. A PLS algorithm was trained on 2 independent training sets (cohorts 1 and 2) and applied to cohort 3. The input vector consisted of MRI values and the target variable was lumen and epithelium density. The algorithm was trained lesion-wise. Trained PiCT models were applied to the test cohort voxel-wise to generate 2 new image contrasts. Mean lesion values were compared between high grade, low grade, and healthy tissue using an ANOVA. An ROC analysis was performed lesion-wise on the test set. RESULTS/ANTICIPATED RESULTS: Results: The segmentation accuracy validation revealed R=0.99 and R=0.72 (p<0.001) for lumen and epithelium, respectively. The co-registration accuracy revealed a 94.5% overlap. The learning curve stabilized at 10 patients with a root mean square error of 0.14, thus the size of the 2 independent training cohorts was set to 10, leaving 19 for the test cohort. DISCUSSION/SIGNIFICANCE OF IMPACT: We present a technique for combining radiology and pathology with machine learning for generating predictive cytological topography (PiCT) maps of cellularity and lumen density prostate. The voxel-wise approach to mapping cellular features generates 2 new interpretable image contrasts, which can potentially increase confidence in diagnosis or guide biopsy and radiation treatment.
The crystal structure of the high-pressure phase-II of cristobalite has been solved by neutron diffraction (space group P21/c, a = 8.3780(11) Å, b = 4.6018(6) Å, c = 9.0568(13) Å, β = 124.949(7)°, at P = 3.5 GPa). This phase corresponds to a distortion of the high-temperature cubic β-phase, rather than of the ambient temperature and pressure tetragonal α-phase.
The commissioning and operation of apparatus for neutron diffraction at simultaneous high temperatures and pressures is reported. The basic design is based on the Paris-Edinburgh cell using opposed anvils, with internal heating. Temperature is measured using neutron radiography. The apparatus has been shown in both on-line and off-line tests to operate to a pressure of 7 GPa and temperature of 1700°C. The apparatus has been used in a neutron diffraction study of the crystal structure of deuterated brucite, and results for 520°C and 5.15 GPa are presented. The diffraction data that can be obtained from the apparatus are of comparable quality to previous high-pressure studies at ambient temperatures, and are clearly good enough for Rietveld refinement analysis to give structural data of reasonable quality.
Total neutron scattering measurements, analysed using a modification of the reverse Monte Carlo modelling method to account for long-range crystallographic order, have been used to describe the temperature-dependent behaviour of the structure of quartz. Two key observations are reported. First, the symmetry change associated with the displacive α–β phase transition is observed in both the long-range and short-range structural correlations. Secondly, some aspects of the structure, such as the Si–O bond length and the thermally-induced dynamic disorder, the latter of which sets in significantly below the transition, are relatively insensitive to the phase transition. These results are used to show that the α-domain model of the β-phase disorder is inappropriate and that the classical soft-mode picture of the phase transition is too simplistic. Instead, it is argued that the structural behaviour is best described in terms of its ability to respond to low-frequency, high-amplitude vibrational modes. This view is supported by additional single-crystal diffuse neutron scattering measurements.