760 research outputs found
Monte Carlo simulations of a scintillation camera using GATE: validation and application modelling
Revisiting methodological issues in transcript analysis: Negotiated coding and reliability
Transcript analysis is an important methodology to study asynchronous online educational discourse. The purpose of this study is to revisit reliability and validity issues associated with transcript analysis. The goal is to provide researchers with guidance in coding transcripts. For validity reasons, it is suggested that the first step is to select a sound theoretical model and coding scheme. Particular focus is placed on exploring the advantages of the option of a negotiated approach to coding the transcript. It is concluded that researchers need to consider the advantages of negotiation when coders and researchers are not familiar with the coding scheme
ĆĆ©n onderzoek is gĆ©Ć©n onderzoek : het belang van replicaties voor de psychologische wetenschap
Recent criticisms on the way psychologists analyze their data, as well as cases of scientific fraud, have led both researchers and the general public to question the reliability of psychologicalresearch. At the same time, researchers have an excellent tool at their disposal to guarantee the robustness of scientific findings: replication studies. Why do researchers rarely perform replication studies? We explain why p-values for single studies fail to provideany indication of whether observed effects are real or not. Onlycumulative science, where important effects are demonstratedrepeatedly, is able to address the challenge to guarantee thereliability of psychological findings. We highlight some novelinitiatives, such as the Open Science Framework, that aim tounderline the importance of replication studies
Design and characterization of dielectric filled TM microwave cavities for ultrafast electron microscopy
Microwave cavities oscillating in the TM mode can be used as dynamic
electron-optical elements inside an electron microscope. By filling the cavity
with a dielectric material it becomes more compact and power efficient,
facilitating the implementation in an electron microscope. However, the
incorporation of the dielectric material makes the manufacturing process more
difficult. Presented here are the steps taken to characterize the dielectric
material, and to reproducibly fabricate dielectric filled cavities. Also
presented are two versions with improved capabilities. The first, called a
dual-mode cavity, is designed to support two modes simultaneously. The second
has been optimized for low power consumption. With this optimized cavity a
magnetic field strength of 2.84 0.07 mT was generated at an input power
of 14.2 0.2 W. Due to the low input powers and small dimensions, these
dielectric cavities are ideal as electron-optical elements for electron
microscopy setups
A dual-time-window protocol to reduce acquisition time of dynamic tau PET imaging using [F-18]MK-6240
Background [F-18]MK-6240 is a PET tracer with sub-nanomolar affinity for neurofibrillary tangles. Therefore, tau quantification is possible with [F-18]MK-6240 PET/CT scans, and it can be used for assessment of Alzheimer's disease. However, long acquisition scans are required to provide fully quantitative estimates of pharmacokinetic parameters. Therefore, on the present study, dual-time-window (DTW) acquisitions was simulated to reduce PET/CT acquisition time, while taking into consideration perfusion changes and possible scanning protocol non-compliance. To that end, time activity curves (TACs) representing a 120-min acquisition (TAC(120)) were simulated using a two-tissue compartment model with metabolite corrected arterial input function from 90-min dynamic [F-18]MK-6240 PET scans of three healthy control subjects and five subjects with mild cognitive impairment or Alzheimer's disease. Therefore, TACs corresponding to different levels of specific binding were generated and then various perfusion changes were simulated. Next, DTW acquisitions were simulated consisting of an acquisition starting at tracer injection, a break and a second acquisition starting at 90 min post-injection. Finally, non-compliance with the PET/CT scanning protocol were simulated to assess its impact on quantification. All TACs were quantified using reference Logan's distribution volume ratio (DVR) and standardized uptake value ratio (SUVR90) using the cerebellar cortex as reference region. Results It was found that DVR from a DTW protocol with a 60-min break between two 30-min dynamic scans closely approximates the DVR from the uninterrupted TAC(120), with a regional bias smaller than 2.5%. Moreover, SUVR90 estimates were more susceptible (regional bias</p
Performance model for āJust-in-Timeā problems in real-time multimedia applications
Over the last few years, the use of large-scale
multimedia data applications has been growing tremendously,
and this growth is not likely to slow down in the near future.
Many multimedia applications operate in a real-time environment
(e.g., surveillance cameras, iris scans), which must meet strict
time constraints, i.e. to analyze video frames at the same rate as
a camera produces them. To meet this requirement, Grid computing
is rapidly becoming indispensable. However, the variabilities
of the software and the hardware in grid environment cause
the strong burstiness in the transmission delay of video frames.
Because the burstiness is unknown beforehand, it is difficult to
determine the right sending moments of video frames. If the
time interval between sending two sequential frames is too large,
then the service utilization may be low. If use large buffer to
guarantee the service utilization, then video frames may be outof-
date because of the long waiting time at buffer in the server
side. This problem is referred to as āJust-in-timeā problem. To
solve this problem, it is essential to determine the right sending
moments of video frames, properly dealing with the trade-off
between the service utilization and the āup-to-dateā of video
frames.
Motivated by this, in this paper we develop an adaptive control
method that react to the continuously changing circumstances in
grid system so as to obtain the highest service utilization on the
one hand and to keep the video frame up-to-date on the other
hand. Extensive experimental validation in our DAS-3 testbed
and the trace-driven simulation show that our method is indeed
highly effective
Getting lost in a story: how narrative engagement emerges from narrative perspective and individual differences in alexithymia
The present research examines how narrative engagement, or the extent to which people immerse themselves into the world of a story, varies as a function of narrative perspective and individual differences in alexithymia. The authors hypothesised that narrative engagement would be higher when people assume a first-person (rather than third-person) perspective and for people lower (rather than higher) on alexithymia. In an online study (N = 541) and a lab study (N = 55), participants with varying levels of alexithymia read first- and/or third-person narrated texts and then rated their narrative engagement. As expected, first-person stories evoked more narrative engagement than third-person stories, and global alexithymia was negatively correlated with narrative engagement. Narrative perspective did not interact with cognitive facets of alexithymia (i.e. difficulties identifying, verbalising, and understanding feelings). However, narrative perspective did interact with affective facets of alexithymia (i.e. emotionalising and fantasising): First-person (rather than third-person) stories elicited more narrative engagement at lower levels of affective alexithymia, but not at higher levels of affective alexithymia. The interaction effect was significant in Study 1; the interaction was significant in Study 2 after controlling for trait absorption. Together, these findings suggest that alexithymia is linked to difficulties in mentally simulating narrative worlds.Pathways through Adolescenc
The Euro Diffusion Project
From 1st January 2002 we have the unique possibility to follow the spread of national euro coins over the different European countries. We model and analyse this movement and estimate the time it will take before on average half the coins in our wallet will be foreign
Risk factors for Mycobacterium tuberculosis infection in 2-4 year olds in a rural HIV-prevalent setting.
BACKGROUND: Mycobacterium tuberculosis infection in children acts as a sentinel for infectious tuberculosis. OBJECTIVE: To assess risk factors associated with tuberculous infection in pre-school children. METHOD: We conducted a population-wide tuberculin skin test (TST) survey from January to December 2012 in Malawi. All children aged 2-4 years residing in a demographic surveillance area were eligible. Detailed demographic data, including adult human immunodeficiency virus (HIV) status, and clinical and sociodemographic data on all diagnosed tuberculosis (TB) patients were available. RESULTS: The prevalence of M. tuberculosis infection was 1.1% using a TST induration cut-off of 15 mm (estimated annual risk of infection of 0.3%). The main identifiable risk factors were maternal HIV infection at birth (adjusted OR [aOR] 3.6, 95%CI 1.1-12.2), having three or more adult members in the household over a lifetime (aOR 2.4, 95%CI 1.2-4.8) and living in close proximity to a known case of infectious TB (aOR 1.6, 95%CI 1.1-2.4), modelled as a linear variable across categories (>200 m, 100-200 m, <100 m, within household). Less than 20% of the infected children lived within 200 m of a known diagnosed case. CONCLUSION: Household and community risk factors identified do not explain the majority of M. tuberculosis infections in children in our setting
Clinical outcomes after first-line HIV treatment failure in South Africa: the next cascade of care
Introduction
There is limited literature on the appropriateness of viral load (VL) monitoring and management of detectable VL in public health settings in rural South Africa.
Methods
We analysed data captured in the electronic patient register from HIVāpositive patients ā„ 15 years old initiating antiretroviral therapy (ART) in 17 public sector clinics in rural KwaZuluāNatal, during 2010ā2016. We estimated the completion rate for VL monitoring at 6, 12, and 24 months. We described the cascade of care for those with any VL measurement ā„ 1000 HIVā1 RNA copies/mL after ā„ 20 weeks on ART, including the following proportions: (1) repeat VL within 6 months; (2) reāsuppressed; (3) switched to secondāline regimen.
Results
There were 29 384 individuals who initiated ART during the period [69% female, median age 31 years (interquartile range 25ā39)]. Of those in care at 6, 12, and 24 months, 40.7% (9861/24 199), 34% (7765/22 807), and 25.5% (4334/16 965) had a VL test at each recommended timeāpoint, respectively. The VL results were documented at all recommended timeāpoints for 12% (2730/22 807) and 6.2% (1054/16 965) of ARTātreated patients for 12 and 24 months, respectively. Only 391 (18.3%) of 2135 individuals with VL ā„ 1000 copies/mL on firstāline ART had a repeat VL documenting reāsuppression or were appropriately changed to secondāline with persistent failure. Completion of the treatment failure cascade occurred a median of 338 days after failure was detected.
Conclusion
We found suboptimal VL monitoring and poor responses to virologic failure in publicāsector ART clinics in rural South Arica. Implications include increased likelihood of morbidity and transmission of drugāresistant HIV
- ā¦