25 research outputs found
Photoelectron diffraction: from phenomenological demonstration to practical tool
The potential of photoelectron diffractionâexploiting the coherent interference of directly-emitted and elastically scattered components of the photoelectron wavefield emitted from a core level of a surface atom to obtain structural informationâwas first appreciated in the 1970s. The first demonstrations of the effect were published towards the end of that decade, but the method has now entered the mainstream armoury of surface structure determination. This short review has two objectives: First, to outline the way that the idea emerged and the way this evolved in my own collaboration with Neville Smith and his colleagues at Bell Labs in the early years: Second, to provide some insight into the current state-of-the art in application of (scanned-energy mode) photoelectron diffraction to address two key issue in quantitative surface structure determination, namely, complexity and precision. In this regard a particularly powerful aspect of photoelectron diffraction is its elemental and chemical-state specificity
Cianoacrilato na colagem de BrĂĄquetes ortodĂ´nticos em resina acrĂlica: hĂĄ maior adesĂŁo?
Pacientes em tratamento ortodĂ´ntico apresentam restauraçþes provisĂłrias com frequĂŞncia. No entanto, poucos estudos avaliam a influĂŞncia dos adesivos na resistĂŞncia ao cisalhamento dos brĂĄquetes nessas superfĂcies. A resina acrĂlica ĂŠ comumente indicada para colagem de brĂĄquetes, porĂŠm o uso do cianoacrilato como adesivo ortodĂ´ntico ĂŠ uma opção analisada. O objetivo do presente trabalho foi avaliar o desempenho do cianoacrilato associado aos materiais comumente utilizados para a fixação de brĂĄquetes metĂĄlicos em restauraçþes provisĂłrias de resina acrĂlica. Quarenta amostras em resina acrĂlica foram preparadas e as superfĂcies homogeinizadas com lixas de carboneto de silĂcio (320 e 600). Em seguida, as amostras foram divididas aleatoriamente em quatro grupos (n=10) com base no tratamento de superfĂcie e agente de uniĂŁo: G1 - brĂĄquetes colados com resina acrĂlica; G2 - brĂĄquetes colados com resina acrĂlica e aplicação de cianoacrilato; G3 - brĂĄquetes colados com Transbond(tm) XT; G4 - brĂĄquetes colados com Transbond(tm) XT e aplicação de cianoacrilato. Foram utilizados brĂĄquetes ortodĂ´nticos de aço inoxidĂĄvel, prescrição Roth, Kirium (3M/Abzil) para incisivos centrais superiores direitos, slot 022. ApĂłs colagem, as amostras foram submetidas ao teste de cisalhamento a uma velocidade de 0,5mm/min em uma mĂĄquina de ensaios universal (EMIC DL-1000). Os dados foram coletados e submetidos Ă anĂĄlise estatĂstica pelo teste ANOVA com nĂvel de significância de 5%. A associação de resina acrĂlica ao cianoacrilato (G2) resultou na maior resistĂŞncia ao cisalhamento (13,76 MPa), mas nĂŁo significativa em comparação aos valores obtidos para a resina acrĂlica (G1= 7,76 MPa). O mesmo pĂ´de ser observado para a associação Transbond(tm) XT e cianoacrilato (G4= 4,03 MPa) em relação a utilização da Transbond(tm) XT de forma isolada (G3= 3,87 MPa) e resina acrĂlica. O tratamento de superfĂcie tem efeito significativo na resistĂŞncia da uniĂŁo dos brĂĄquetes colados aos materiais provisĂłrios. A associação de cianoacrilato ao monĂ´mero de metilmetacrilato apresentou maior resistĂŞncia ao cisalhamento, sendo mais indicada clinicamente
Reproducibility in the absence of selective reporting : An illustration from large-scale brain asymmetry research
Altres ajuts: Max Planck Society (Germany).The problem of poor reproducibility of scientific findings has received much attention over recent years, in a variety of fields including psychology and neuroscience. The problem has been partly attributed to publication bias and unwanted practices such as p-hacking. Low statistical power in individual studies is also understood to be an important factor. In a recent multisite collaborative study, we mapped brain anatomical left-right asymmetries for regional measures of surface area and cortical thickness, in 99 MRI datasets from around the world, for a total of over 17,000 participants. In the present study, we revisited these hemispheric effects from the perspective of reproducibility. Within each dataset, we considered that an effect had been reproduced when it matched the meta-analytic effect from the 98 other datasets, in terms of effect direction and significance threshold. In this sense, the results within each dataset were viewed as coming from separate studies in an "ideal publishing environment," that is, free from selective reporting and p hacking. We found an average reproducibility rate of 63.2% (SD = 22.9%, min = 22.2%, max = 97.0%). As expected, reproducibility was higher for larger effects and in larger datasets. Reproducibility was not obviously related to the age of participants, scanner field strength, FreeSurfer software version, cortical regional measurement reliability, or regional size. These findings constitute an empirical illustration of reproducibility in the absence of publication bias or p hacking, when assessing realistic biological effects in heterogeneous neuroscience data, and given typically-used sample sizes
Using structural MRI to identify bipolar disorders - 13 site machine learning study in 3020 individuals from the ENIGMA Bipolar Disorders Working Group.
Bipolar disorders (BDs) are among the leading causes of morbidity and disability. Objective biological markers, such as those based on brain imaging, could aid in clinical management of BD. Machine learning (ML) brings neuroimaging analyses to individual subject level and may potentially allow for their diagnostic use. However, fair and optimal application of ML requires large, multi-site datasets. We applied ML (support vector machines) to MRI data (regional cortical thickness, surface area, subcortical volumes) from 853 BD and 2167 control participants from 13 cohorts in the ENIGMA consortium. We attempted to differentiate BD from control participants, investigated different data handling strategies and studied the neuroimaging/clinical features most important for classification. Individual site accuracies ranged from 45.23% to 81.07%. Aggregate subject-level analyses yielded the highest accuracy (65.23%, 95% CIâ=â63.47-67.00, ROC-AUCâ=â71.49%, 95% CIâ=â69.39-73.59), followed by leave-one-site-out cross-validation (accuracy = 58.67%, 95% CIâ=â56.70-60.63). Meta-analysis of individual site accuracies did not provide above chance results. There was substantial agreement between the regions that contributed to identification of BD participants in the best performing site and in the aggregate dataset (Cohen's Kappaâ=â0.83, 95% CIâ=â0.829-0.831). Treatment with anticonvulsants and age were associated with greater odds of correct classification. Although short of the 80% clinically relevant accuracy threshold, the results are promising and provide a fair and realistic estimate of classification performance, which can be achieved in a large, ecologically valid, multi-site sample of BD participants based on regional neurostructural measures. Furthermore, the significant classification in different samples was based on plausible and similar neuroanatomical features. Future multi-site studies should move towards sharing of raw/voxelwise neuroimaging data
Subcortical volumes across the lifespan: data from 18,605 healthy individuals aged 3-90 years
Age has a major effect on brain volume. However, the normative studies available are constrained by small sample sizes, restricted age coverage and significant methodological variability. These limitations introduce inconsistencies and may obscure or distort the lifespan trajectories of brain morphometry. In response, we capitalized on the resources of the Enhancing Neuroimaging Genetics through Meta-Analysis (ENIGMA) Consortium to examine age-related trajectories inferred from cross-sectional measures of the ventricles, the basal ganglia (caudate, putamen, pallidum, and nucleus accumbens), the thalamus, hippocampus and amygdala using magnetic resonance imaging data obtained from 18,605 individuals aged 3-90 years. All subcortical structure volumes were at their maximum value early in life. The volume of the basal ganglia showed a monotonic negative association with age thereafter; there was no significant association between age and the volumes of the thalamus, amygdala and the hippocampus (with some degree of decline in thalamus) until the sixth decade of life after which they also showed a steep negative association with age. The lateral ventricles showed continuous enlargement throughout the lifespan. Age was positively associated with inter-individual variability in the hippocampus and amygdala and the lateral ventricles. These results were robust to potential confounders and could be used to examine the functional significance of deviations from typical age-related morphometric patterns.Education and Child Studie
Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures
Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo
Phase I Randomized, Double-Blind Pilot Study of Micronized Resveratrol (SRT501) in Patients with Hepatic MetastasesâSafety, Pharmacokinetics, and Pharmacodynamics
Learning from Post-project Reviews : A Cross-Case Analysis
Every new product development (NPD) project should not only deliver a successful
new product but also should generate learning for the organization. Postproject
reviews (PPRs) are recognized by both practitioners and academics as an
appropriate mechanism to stimulate and capture learning in NPD teams. However,
relatively few companies use PPRs, and those that do use them often fail to do
so effectively. Although they are widely perceived to be a useful tool,
empirical research on how PPRs are typically organized and the learning that
results is limited. The present article addresses this gap in the extant
knowledge and describes five in-depth case studies, which were conducted at
leading companies in Germany. A detailed investigation was made of how PPRs are
conducted and of the type of learning that can result. Three main sources of
data were used for each case: company documentation, in-depth interviews with
managers responsible for NPD, and observation of an actual PPR. The different
data sources enabled extensive triangulation of data to be conducted and a high
degree of reliability and validity to be achieved. The analysis enabled a number
of key characteristics of the way PPRs are managed to be identified. Various
characteristics of PPRs influence their utility, such as the time at which they
take place and the way discussions are moderated. In addition, the data show
that participants in the discussions at PPRs often use metaphors and stories,
which indicates that PPRs have the potential to generate tacit knowledge.
Interestingly, the data also show that there are various different ways in which
metaphors and stories appear to stimulate discussions on NPD projects. Based on
the cross-case analysis, a wide range of implications are identified.
Researchers need to investigate PPRs further to identify how they can generate
tacit and explicit knowledge and support project-to-project learning. The
generation of tacit knowledge in NPD is a topic that particularly needs further
investigation. The research also led to a range of recommendations for
practitioners. Companies need to strongly communicate the purpose and value of
PPRs, to run them effectively to stimulate the maximum possible learning, and to
disseminate the findings widely. PPRs have the potential to create and transfer
knowledge amongst NPD professionals, but, as they are seldom currently used,
many companies are missing an important opportunity
Exercise induced mobilisation of the marginated granulocyte pool in the investigation of ethnic neutropenia
This study was designed to determine whether ethnic neutropenia is caused by an increased proportion of neutrophils being present in the marginated granulocyte pool. Thirty two healthy volunteers, half of whom were African or Afro-Caribbean and half of whom were white, exercised vigorously for 10 minutes on a step machine to mobilise granulocytes from the marginated granulocyte pool into the circulating granulocyte pool. The amount of work performed and the pulse rate response of the two ethnic groups were compared to determine whether the exercise carried out was comparable. A full blood count and an automated differential count were performed before and after the exercise. The haemoglobin concentration, platelet count, and absolute counts of total leucocytes and leucocyte subsets before and after exercise were compared in each individual and the values in the two ethnic groups both before and after exercise were compared. The absolute increase in neutrophils in the two ethnic groups was compared. The African/Afro-Caribbean group was found to have a reduced rather than enhanced ability to mobilise neutrophils from the marginated granulocyte pool. Therefore, increased margination of neutrophils is unlikely to be the cause of ethnic neutropenia. Key Words: ethnic neutropenia ⢠circulating and marginated granulocyte pool ⢠exercis