Browsing by Author "Visser, W."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Determinants of serum 25-hydroxyvitamin D levels in healthy young adults living in the Western Cape, South Africa
    (South African Academy of Family Physicians, 2019-10-28) Visser, Janicke; Knight, K.; Philips, L.; Visser, W.; Wallace, M.; Nel, D. G.; Blaauw, Renee
    Background: Vitamin D deficiency is fast emerging as a global pandemic. In South Africa few studies have been conducted to determine the vitamin D status of the healthy population. Methods: This prospective study with an analytical component investigated vitamin D status of healthy undergraduate students at two time points (winter and summer) at Stellenbosch University. Serum 25(OH)D was determined, anthropometric measurements taken and dietary vitamin D intake estimated (food-frequency questionnaire). Skin tone was determined (Fitzpatrick skin type classification), and a skin reflectometry device used to measure dermal melanin content. Results: Results of 242 students indicated a mean serum 25(OH)D of 63.80 ± 41.35 ng/ml and a high prevalence of vitamin D sufficiency (88%). Significantly more females experienced suboptimal vitamin D levels than males (18 vs. 5%; p < 0.01). Participants with lighter skin tones had higher levels of 25(OH)D than those with darker skin tones (chi-square = 24.02; p = 0.02). The majority (60.74%) had a normal BMI, although there was no significant relationship between BMI and serum 25 (OH)D (Spearman’s r=–0.11; p = 0.09). Total mean dietary vitamin D intake was 7.99 ± 13.81 mcg, with 87.2% having inadequate intake (< 15 mcg). The relationship between total vitamin D intake and serum 25(OH)D was found to be significant in winter (p < 0.001) and summer (p = 0.01). Serum vitamin D levels were significantly higher in the winter phase (p < 0.001). Conclusions: A low prevalence of vitamin D deficiency was found amongst healthy young adults, despite low dietary vitamin D intakes. Significant relationships were found between serum 25(OH)D and gender, skin tone and vitamin D intake. Further studies need to be conducted, especially in high-risk groups, before results are applied to the greater South African public.
  • Thumbnail Image
    Item
    Firegaze : processing and visualizing firewall logs in the cloud
    (SATNAC, 2013) Van Tonder, R.; Visser, W.
    This project aims to visualise packet counts filtered by iptables at the network layer, and allows for performing network forensics in a distributed environment. For example, anomalies such as bandwidth spikes and port scans are exposed and quickly identifiable. Naturally, there are a host of tools which already perform this function. The twist with this project is that it should operate on a scalable cloud infrastructure—Nimbula Director is used as a test bed to this end. Intrusion Detection Systems and full-blown Security Information and Event Management (SIEM) solutions have their merits but are often too bulky. Cloud infrastructures rely principally on correctly configured firewalls for network-layer security. As such, Firegaze is a prototype solution which serves as a supplement to network layer security by visualizing firewall activity; it does not perform any analysis, but rather leaves it up to the system administrator to identify anomalous activity. Typically, log files are only needed once an incident occurs, or in the event of system failure. The idea behind Firegaze was to provide a solution for visualizing iptables logs in real-time, or on a historical basis. The challenge of doing this in an environment which scales has influenced the implementation greatly; logs are propagated among nodes in a hierarchical manner, and logs are inserted into a sharded MongoDB database according to a pre-aggregated reports pattern.