Stability of Weak Confined Wake Behind a Cylinder in Fully Developed Turbulent Channel Flow

AbstractThe motivation for the study of instability of turbulent wake flow in a confined turbulent channel was multi-fold. First, the instability of confined wake flows has not been studied much. Second, confined wakes are found to retain their mean velocity profile for a considerable downstream distance. Third, wakes have two points of inflection, one each on either side of the centre line. The basic aim of the present study was to investigate the correlation between the turbulence in the wake region and the inflection points in the wake region using stability theory. The wake behind a cylinder of diameter d in a turbulent channel with half width h, is a weak confined wake when d/h ≈ 0.2. Thus, d/h=0.2 was chosen for the present work. Experimental results are obtained by introducing organized disturbances in the wake and tracking these downstream. Theoretical results were obtained by solving the Orr-Sommerfeld equation by numerical methods

Clues to understanding sudden infant death : a role for Helicobacter pylori and innate immunity?

In this thesis in pediatric forensic medicine, a series of experimental studies was performed in order to investigate Helicobacter pylori infection and innate immunity in infancy with special regard to Sudden infant death syndrome, SIDS. By a commercial ELISA test, the prevalence of H. pylori carriage in stool of 249 healthy children between 0 and 3 years of age was investigated. A high detection rate was found in neonates related to mode of delivery, indicating that transfection from mother to child is likely. In infants older than one week of age, the H. pylori carriage rate was 8%. In a subsequent study of 160 victims of sudden death, H. pylori carriage was significantly associated with SIDS and infections: 25% of the SIDS victims and 53% of the infants who died from infectious disease were H. pylori positive. Moreover, H. pylori carriage in SIDS victims was associated with central immune response, assessed by high Interleukin-6 levels in cerebrospinal fluid. Surfactant protein A (SP-A), surfactant protein D (SP-D) and mannose-binding lectin (MBL) are proteins of innate immunity involved in the first-line defense against microbial agents. By immunohistochemistry, a method was established to enable semi-quantitative evaluation of SP-A and SP-D expression in post-mortem tissues from fetal to adult life. In lung tissue, an unpredicted drop in SP-A expression was demonstrated in infants between 1 week and 5 months of age, corresponding with the peak period for SIDS. This drop may imply that down-regulation of SP-A occurs in normal post-natal development. Later genotyping of the SP-A, SP-D and MBL genes revealed no significant association between genetic polymorphisms and SIDS compared to explained infant deaths. Thesis conclusion: During a vulnerable age period in post-natal life, H. pylori infection may add to the microbial load and trigger the death mechanism in SIDS. A drop in SP-A expression may contribute to this vulnerability

Norwegian parents avoid placing infants in prone sleeping positions but frequently share beds in hazardous ways

Aim Campaigns to prevent prone sleeping and other modifiable risk factors have greatly reduced the incidence of sudden infant death syndrome in Norway. Sleep-related infant deaths still occur sporadically and may be preventable. We studied infants’ sleeping environments and whether parents followed safe sleep recommendations. Methods Parents with infants up to 12 months of age were invited to complete an online questionnaire from May to December 2018. It was publicised by health centres and on websites and social media. Results We received 4886 responses and 4150 met the age criteria and were included. Just under two-thirds (62.7%) reported routine bed-sharing, and this practice was associated with increased nocturnal breastfeeding, single parents and having more than one child. A small number of infants under six months were occasionally placed prone when they were laid down to sleep (2.1%) and 29.7% were placed on their side. Nearly three-quarters (72.6%) of the 2330 parents with infants under six months of age reported previous high-risk behaviour, such as sleeping together on a sofa or bed-sharing after smoking or drinking. Conclusion Norwegian parents rarely used prone sleeping positions for infants. However, bed-sharing was common, including high-risk scenarios such as smoking, alcohol use and sofas

Awareness and Factors Associated with Health Care Worker’s Knowledge on Rubella Infection: A Study after the Introduction of Rubella Vaccine in Tanzania

Background Congenital rubella syndrome is a global health problem. The incidence is much higher in Africa and Southeast Asia than the rest of the world, especially in countries where universal rubella vaccination has not been implemented. Healthcare worker’s knowledge on rubella infection and the rubella vaccine is of utmost importance in achieving and maintaining vaccination coverage targets. This study aimed to assess health care workers knowledge on rubella infection in Kilimanjaro Tanzania, after the introduction of a rubella vaccination. Methods This was a health facility-based cross sectional study. It was conducted in three districts of the Kilimanjaro region between August and October 2016. The study involved eligible health care workers in selected health facilities. An interview guide was used for collecting information by face-to-face interviews. Multivariate analysis was used to assess factors associated with rubella knowledge among healthcare workers. Results A total of 126 health care workers were interviewed. An acceptable level of knowledge was considered if all five questions about rubella were correctly answered. Only 26.4% (n = 31) answered all questions correctly. In multivariate analysis education level and working department were predictors of rubella knowledge; health care workers with an advanced diploma had an adjusted odds ratio (AOR) of 7.7 (95% Confidence interval; CI: 1.4, 41.0), those with a university degree (AOR: 10; 95% CI: 2.4; 42.5) and health care workers in the outpatient department (AOR: 0.06; 95% CI: 0.04; 0.29). Conclusions Our study confirmed that health care worker’s knowledge on rubella infection was low in the areas where rubella vaccination had been introduced. We recommend continuous education and supportive supervision post vaccine introduction in order to increase healthcare worker’s knowledge on rubella infection, congenital rubella syndrome and prevention through sustained high vaccination coverage

A roadmap to the safe practice of forensic medicine in the COVID-19 pandemic

The COVID-19 pandemic has forced forensic practitioners to consider how we perform our normal duties, especially when those duties involve humans. The potential for contracting the virus from working in close contact with living sufferers is high, and we have yet to fully determine the risk of infection from the deceased. In an attempt to support the community, the Journal of Forensic & Legal Medicine has drawn together three articles which underline the importance of continued forensic medical practice during the pandemic and highlight some factors to consider in a Roadmap towards safe practice. Our Roadmap has intentionally taken an international perspective and supports other work we have published in the Journal on our collective response to the COVID-19 crisis.Peer reviewe

A Weighted Histogram-Based Tone Mapping Algorithm for CT images

Computed Tomography (CT) images have a high dynamic range, which makes visualization challenging. Histogram equalization methods either use spatially invariant weights or limited kernel size due to the complexity of pairwise contribution calculation. We present a weighted histogram equalization-based tone mapping algorithm which utilizes Fast Fourier Transform for distance-dependent contribution calculation and distance-based weights. The weights follow power-law without distance-based cut-off. The resulting images have good local contrast without noticeable artefacts. The results are compared to eight popular tone mapping operators

Image De-Quantization Using Plate Bending Model

Discretized image signals might have a lower dynamic range than the display. Because of this, false contours might appear when the image has the same pixel value for a larger region and the distance between pixel levels reaches the noticeable difference threshold. There have been several methods aimed at approximating the high bit depth of the original signal. Our method models a region with a bended plate model, which leads to the biharmonic equation. This method addresses several new aspects: the reconstruction of non-continuous regions when foreground objects split the area into separate regions; the incorporation of confidence about pixel levels, making the model tunable; and the method gives a physics-inspired way to handle local maximal/minimal regions. The solution of the biharmonic equation yields a smooth high-order signal approximation and handles the local maxima/minima problems

How different iterative and filtered back projection kernels affect CT numbers and low contrast detectability

Objective: The aim of this study was to evaluate how different iterative and filtered back projection kernels affect the computed tomography (CT) numbers and low contrast detectability. Methods: Five different scans were performed at 6 different tube potentials on the same Catphan 600 phantom using approximately the same dose level and otherwise identical settings. The scans were reconstructed using all available filtered back projection body kernels and with iterative reconstruction techniques. Results: The CT numbers and the contrast-to-noise ratios were reported and how they are affected by the kernel choice and strength of iterative reconstruction. Conclusions: Iterative reconstruction improved contrast-to-noise ratio in most cases, but in certain situations, it decreased it. Variations in CT numbers can be large between kernels with similar sharpness for certain densities

Applicability of a clinical cardiac CT protocol in post mortem studies

Objective Confirmation whether an optimized clinical cardiac CT scan protocol is also optimal for post mortem cardiac CT scans without iodine contrast or the reconstruction parameters should be changed. Materials and methods 27 CT volumes (three cases for three recon- struction kernel with three different iterative reconstruction settings) were graded by six readers in order to find the optimal reconstruction parame- ters. The scans were performed on a Siemens Definition Flash CT scanner using 120 kV tube potentials. Results The study has shown that from the investigated options the softest cardiac kernel with the strongest iterative reconstruction were pre- ferred by the readers (I26 Safire 3). Conclusion The results indicate that the scan protocol which was adopted from clinical practice is applicable in forensic radiology too even though iodine contrast agent was not administered

A Weighted Histogram-Based Tone Mapping Algorithm for CT images

Computed Tomography (CT) images have a high dynamic range, which makes visualization challenging. Histogram equalization methods either use spatially invariant weights or limited kernel size due to the complexity of pairwise contribution calculation. We present a weighted histogram equalization-based tone mapping algorithm which utilizes Fast Fourier Transform for distance-dependent contribution calculation and distance-based weights. The weights follow power-law without distance-based cut-off. The resulting images have good local contrast without noticeable artefacts. The results are compared to eight popular tone mapping operators