Sebastian Arndt

A Critical Assessment of Li/MgO-Based Catalysts for the Oxidative Coupling of Methane

Li/MgO is one of the most frequently investigated catalysts for the oxidative coupling of methane. Besides catalytic testing, it is also a suitable system to perform surface science experiments and quantum chemical calculations, which is not possible for many other active catalysts. However, the real structure of Li/MgO, the nature of the active center and the structure - activity relationship remain unclear, despite all the research that has been done. The aim of this review is to summarize the available knowledge on Li/MgO to structure and accelerate and improve the ongoing work on this catalytic system.

Analyzing Speech Quality Perception Using Electroencephalography

Common speech quality evaluation methods rely on self-reported opinions after perceiving test stimuli. Whereas these methods-when carefully applied-provide valid and reliable quality indices, they provide little insight into the processes underlying perception and judgment. In this paper, we analyze the performance of electroencephalography (EEG) for indicating different types of degradations in speech stimuli. We show that a certain EEG technique, event-related-potentials (ERP) analysis, is a useful and valid tool in quality research. Three experiments are reported which show that quality degradations can be monitored in conscious and presumably non-conscious stages of processing. Potential and limitations of the approach are discussed and lines of future research are drawn.

Using Electroencephalography to Measure Perceived Video Quality

Using less bandwidth on the one hand and delivering high quality content on the other hand is one of the big goals for video service providers. Standardized rating tests are commonly used to quantify audiovisual quality. In order to better understand the neuronal processes underlying these quality ratings physiological measures may provide insights. This paper shows results of a series of studies using a physiological measurement, namely electroencephalography (EEG), combined with standard rating methods. The experiments follow an incremental approach in stimuli selection, ranging from purely visual to audiovisual stimuli. Results show that EEG is a feasible complement measurement technique to assess audiovisual quality as we achieve high correlation values between subjective and physiological data consistently through all experiments.

Perception of low-quality videos analyzed by means of electroencephalography

The subjective evaluation of video quality mostly relies on opinion tests in which test participants judge perceived quality on rating scales. However, these methods provide limited insight how the quality judgments are being formed in the brain. In past studies we showed the general feasibility to complement opinion tests with physiological measures, as the electroencephalography (EEG), for pure video and audio experiments. To establish EEG as a reliable complement measurement method in standard quality rating tests, the next step is to validate the method in the audiovisual domain. For this purpose we conducted an experiment using audiovisual stimuli and degraded these in both modalities. We show that the more degraded a video is the earlier and higher the P300 amplitude is rising. In addition, the peak amplitudes are highly correlated with the audiovisual Mean Opinion Score (MOS).

Psychophysiology-Based QoE Assessment: A Survey

We present a survey of psychophysiology-based assessment for quality of experience (QoE) in advanced multimedia technologies. We provide a classification of methods relevant to QoE and describe related psychological processes, experimental design considerations, and signal analysis techniques. We summarize multimodal techniques and discuss several important aspects of psychophysiology-based QoE assessment, including the synergies with psychophysical assessment and the need for standardized experimental design. This survey is not considered to be exhaustive but serves as a guideline for those interested to further explore this emerging field of research.

Too tired for calling? A physiological measure of fatigue caused by bandwidth limitations

Common methods to determine the quality of media rely on conscious ratings of a subjects opinion about the quality of presented stimuli. While such methods provide a reliable and valid means of determining quality, they provide little insight into the physiological processes preceding the quality judgment, which, however, may affect the subjective behavior, e.g., in terms of alertness or media usage duration. In this paper we used a non-intrusive physiological method, electroencephalography, to assess the cognitive state of subjects related to the quality of auditory speech stimuli. We show that users listening to degraded audio rated the quality lower in comparison to an undisturbed stimulus as expected and, in addition, got more fatigued during the 20 minute presentation. Indicators of the increased fatigue were Theta and Alpha frequencies of the electroencephalogram data. The results show that the perception of degraded media has long-term influences on physiological processes at the time scale of minutes which may immediately influence customer behavior.

Feasibility study of the Mn–Na2WO4/SiO2 catalytic system for the oxidative coupling of methane in a fluidized-bed reactor

The catalytic system Mn–Na2WO4/SiO2, known for its relatively stable performance for oxidative coupling of methane (OCM), has been thoroughly investigated in the past. In order to evaluate its catalytic performance, micro-fixed-bed reactors were used almost exclusively. This study aims to answer the question of whether this catalytic system would be applicable on a larger scale using a miniplant fluidized-bed quartz glass reactor. Special consideration was given for finding the optimal operating conditions and investigating whether catalyst abrasion and agglomeration could be limiting factors. In this study different compositions of the Mn–Na2WO4/SiO2 catalyst were tested. High sodium content catalysts were difficult to fluidize at the optimal reaction temperature due to severe agglomeration by melting. Low sodium content catalysts showed low selectivity to C2+ hydrocarbons. Catalysts containing intermediate levels of sodium were used for detailed testing as they showed promising performance as well as good fluidizability. The influence of the different reaction parameters on performance was tested, resulting in 19.4% C2 yield at 40% C2 selectivity. Catalysts before and after reaction were characterized regarding composition, crystalline phases, surface morphology and thermal stability. After time on stream, all catalysts exhibited a reduction in specific surface area, changes in Mn valence state (Mnδ+ (2 ≤ δ ≤ 3)) and changes in morphology due to grain growth.

Brain Activity Correlates of Quality of Experience

This chapter outlines common brain activity correlates that are known from neuroscience, gives an overview on established electrophysiological analysis methods and on the background of electroencephalography (EEG). After that an overview on study designs will be given and a practical guideline for the design of experiments using EEG in the research area of Quality of Experience (QoE) will be presented. At the end of this chapter we will close with a summary, give practical advice, and we will outline potential interesting future research topics.

The effects of text-to-speech system quality on emotional states and frontal alpha band power

The tolerance limit for acceptable multimedia quality is changing as more and more high quality services approach the market. Thus, negative emotional reactions towards low quality services may cause user disappointment and are likely to increase churn rate. The current study analyzes how different levels of synthetic speech quality, obtained from different text-to-speech (TTS) systems, affect the emotional response of a user. This is achieved using two methods: subjective, by means of user reports; and neurophysiological by means of electroencephalography (EEG) analysis. More specifically, we analyzed the frontal alpha band power and correlated this with the subjective ratings based on the Self-Assessment Manikin scale. We found an increase in neuronal activity in the left frontal area with decreasing quality and argue that this is due to user disappointment with low quality TTS systems as they become harder to understand.

Using eye-tracking and correlates of brain activity to predict quality scores

Subjective quality tests give important information about the users perception on the quality of an audio or video signal. These tests are helpful but usually lack information about the users cognitive state. This might be crucial when consuming a service, as lower quality services may lead to a less frequent use. Therefore, physiological measures have become more popular in the domain of quality assessment as they give more detailed insights about e.g. fatigue and attention of a person. In the current study we used spatially degraded videos and obtained 1) standard subjective quality judgments, 2) eye movement parameters and 3) brain activity using electroencephalography (EEG). The results indicate more focused attention on the degraded area once participants found that area, as pupil diameter increases and the proportion of alpha activity decreases. On the basis of the data a model is proposed which predicts the quality scores from the obtained physiological measures.