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Browsing by Author "Levitski, Andres"

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  • Building Distributed File Systems on Commercial Cloud Storage Services 
    Levitski, Andres (2016)
    With the increase in bandwidths available for internet users, cloud storage services have emerged to offer home users an easy way to share files and extend the storage space available for them. Most systems offer a limited free storage quota and combining these resources from multiple providers could be intriguing to cost-oriented users. In this study, we will implement a virtual file system that utilizes multiple different commercial cloud storage services (Dropbox, Google Drive, Microsoft OneDrive) to store its data. The data will be distributed among the different services and the structure of the data will be managed locally by the file system. The file system will be run in user space using FUSE and will use APIs provided by the cloud storage services to access the data. Our goal is to show that it is feasible to combine the free space offered by multiple services into a single easily accessible storage medium. Building such a system requires making design choices in multiple problem areas ranging from data distribution and performance to data integrity and data security. We will show how our file system is designed to address these requirements and will then conduct several tests to measure and analyze the level of performance provided by our system in different file system operation scenarios. The results will also be compared to the performance of using the distinct cloud storage services directly without distributing the data. This will help us to estimate the overhead or possible gain in performance caused by the distribution of data. It will also help us to locate the bottlenecks of the system. Finally, we will discuss some of the ways that could be used to improve the system based on test results and examples from existing distributed file systems.
  • Effects of fatigue on driver performance on slippery roads 
    Levitski, Andres (2020)
    Objectives Fatigue is a major factor affecting driving performance and traffic accident risk. Driving conditions influence how people experience fatigue while driving. Driving in demanding conditions may increase vigilance in tired drivers; however, it may also increase cognitive load and become an additional source of fatigue. The current study investigated how driving on a slippery road interacts with fatigue caused by sleep deprivation and how it influences driving performance. Methods Twelve male participants (aged 19–21) drove 52.5 km in a driving simulator in four different conditions (day vs night and dry vs slippery road). Subjective sleep-related fatigue was measured with the Karolinska Sleepiness Scale and physiological fatigue in blink durations with electro-oculography. Three measures were used for driver performance: standard deviation of lateral position, mean steering wheel movement amplitude and mean steering wheel movement peak velocity. After each driving session, participants negotiated a cone track. The success rate for this task was analysed separately. Results Driving on slippery roads improved performance in all three performance metrics in sleep-deprived drivers. The three-way interaction between driver condition, road condition and time-on-task was significant for subjective sleep-related fatigue but not for performance. Sleep-deprived drivers became increasingly sleepy over time when driving in slippery conditions; however, this did not negatively affect their performance. Conclusions Driving in demanding weather conditions can increase the fatigue experienced by drivers; however, this change may not be initially detectable in performance. Large individual variability in response to both fatigue and driving conditions requires further research.

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