In this article, I examine the source of the photoplethysmograph (PPG), as well as methods of investigation, with an emphasize on amplitude, rhythm, and pulse analysis. The PPG waveform was first ...described in the 1930s. Although considered an interesting ancillary monitor, the "pulse waveform" never underwent intensive investigation. Its importance in clinical medicine was greatly increased with the introduction of the pulse oximeter into routine clinical care in the 1980s. Its waveform is now commonly displayed in the clinical setting. Active research efforts are beginning to demonstrate a utility beyond oxygen saturation and heart rate determination. Future trends are being heavily influenced by modern digital signal processing, which is allowing a re-examination of this ubiquitous waveform. Key to unlocking the potential of this waveform is an unfettered access to the raw signal, combined with standardization of its presentation, and methods of analysis. In the long run, we need to learn how to consistently quantify the characteristics of the PPG in such a way as to allow the results from research efforts be translated into clinically useful devices.
In this work, we present a general theoretical and numerical approach for simultaneously solving the photovoltage and photocurrent at semiconductor–liquid interfaces. Our methodology extends ...drift-diffusion methods developed for metal–semiconductor Schottky contacts in the device physics community into the domain of semiconductor–liquid “pseudo-Schottky” contacts. This model is applied to the study of photoelectrochemical anodes, utilized in the oxidative splitting of water. To capture both the photovoltage and photocurrent at semiconductor–liquid interfaces, we show that it is necessary to solve both the electron and hole current continuity equations simultaneously. The electron continuity equation is needed to primarily capture the photovoltage formation at photoanodes, whereas the hole continuity equation must be solved to obtain the photocurrent. Both continuity equations are solved through coupled recombination and generation terms. Moreover, to capture charge transfer at the semiconductor–liquid interface, floating (Neumann) boundary conditions are applied to the electron and hole continuity equations. As a model system, we have studied the illuminated hematite photoanode, where it is shown that our approach can capture band flattening during the formation of a photovoltage, as well as the photocurrent onset and saturation. Finally, the utility of this methodology is demonstrated by correlating our theoretical calculations with photocurrent measurements reported in the literature. In general, this work is intended to expand the scope of photocatalytic device design tools and thereby aid the optimization of solar fuel generation.
Photoplethysmography Alian, Aymen A., M.D; Shelley, Kirk H., M.D., Ph.D
Best practice & research. Clinical anaesthesiology,
12/2014, Letnik:
28, Številka:
4
Journal Article
Recenzirano
The photoplethysmographic (PPG) waveform, also known as the pulse oximeter waveform, is one of the most commonly displayed clinical waveforms. First described in the 1930s, the technology behind the ...waveform is simple. The waveform, as displayed on the modern pulse oximeter, is an amplified and highly filtered measurement of light absorption by the local tissue over time. It is optimized by medical device manufacturers to accentuate its pulsatile components. Physiologically, it is the result of a complex, and not well understood, interaction between the cardiovascular, respiratory, and autonomic systems. All modern pulse oximeters extract and display the heart rate and oxygen saturation derived from the PPG measurements at multiple wavelengths. “As is,” the PPG is an excellent monitor for cardiac arrhythmia, particularly when used in conjunction with the electrocardiogram (ECG). With slight modifications in the display of the PPG (either to a strip chart recorder or slowed down on the monitor screen), the PPG can be used to measure the ventilator-induced modulations which have been associated with hypovolemia. Research efforts are under way to analyze the PPG using improved digital signal processing methods to develop new physiologic parameters. It is hoped that when these new physiologic parameters are combined with a more modern understanding of cardiovascular physiology (functional hemodynamics) the potential utility of the PPG will be expanded. The clinical researcher's objective is the use of the PPG to guide early goal-directed therapeutic interventions (fluid, vasopressors, and inotropes), in effect to extract from the simple PPG the information and therapeutic guidance that was previously only obtainable from an arterial pressure line and the pulmonary artery catheter.
This exploratory study examined how the level and nature of teaching presence impacted two online forum discussions from three dimensions: participation and interaction, cognitive presence, and ...knowledge development via assimilating peer messages. Effects on participation and interaction were graphically depicted. Effects on cognitive presence and knowledge construction via assimilating messages were suggested via statistical analysis, followed by qualitative interpretations. Twenty‐six tertiary online learners with varied demographic backgrounds participated in the study for 6 weeks. The results showed that the nature of teaching presence in the study, specified to teacher initiation, roles of teaching presence and means of making teaching presence, largely shaped the impact of teaching presence on learning. A higher level of teaching presence was observed to be associated with a lower level of student participation, peer interaction, cognitive presence and learning uptake. Based on the results, implications for integrating and researching teaching presence in computer conferences were provided.
The photovoltage and photocurrent both serve as important design metrics when assessing the performance of photoanodes within photoelectrochemical cells. However, to date, wide disagreement persists ...(even in the recent literature) regarding how the photovoltage should be physically interpreted; this lack of consensus is further coupled to physical interpretations of the photocurrent. In this work, we utilize state-of-the-art device modeling to help clarify the physical origins of both the photovoltage and photocurrent in photoanodes. Our methodology is based on directly solving the governing electron and hole continuity equations, coupled self-consistently with Poisson’s equation, with appropriate boundary conditions. Through a systematic examination of a model photoanode, hematite, we correlate directly measurable current–voltage characteristics with operational band diagrams. It is shown that, by directly mapping specific operating points of either equal current or equal voltage (both illuminated and in the dark) to band diagram plots, one is able to obtain substantial insights into the physical nature of both the photocurrent and photovoltage. Throughout this analysis, the fundamental distinction between electrostatic and electrochemical perturbations under arising illumination is underscored. By aiding the community-wide effort to arrive at a consensus on these concepts, we aim to further enable the design of higher-efficiency photoanodes.
We report on the achievement of wafer-level photocatalytic overall water splitting on GaN nanowires grown by molecular beam epitaxy with the incorporation of Rh/Cr2O3 core–shell nanostructures acting ...as cocatalysts, through which H2 evolution is promoted by the noble metal core (Rh) while the water forming back reaction over Rh is effectively prevented by the Cr2O3 shell O2 diffusion barrier. The decomposition of pure water into H2 and O2 by GaN nanowires is confirmed to be a highly stable photocatalytic process, with the turnover number per unit time well exceeding the value of any previously reported GaN powder samples.
Training and testing diagram: blue lines indicate the training phase to get optimal weights for Q-network; red lines indicate the testing phase using trained Q-network; green lines indicate the ...common steps shared by both training and testing. Display omitted
Energy efficiency remains a significant topic in the control of building heating, ventilation, and air-conditioning (HVAC) systems, and diverse set of control strategies have been developed to optimize performance, including recently emerging techniques of deep reinforcement learning (DRL). While most existing works have focused on minimizing energy consumption, the generalization to energy cost minimization under time-varying electricity price profiles and demand charges has rarely been studied. Under these utility structures, significant cost savings can be achieved by pre-cooling buildings in the early morning when electricity is cheaper, thereby reducing expensive afternoon consumption and lowering peak demand. However, correctly identifying these savings requires planning horizons of one day or more. To tackle this problem, we develop Deep Q-Network (DQN) with an action processor, defining the environment as a Partially Observable Markov Decision Process (POMDP) with a reward function consisting of energy cost (time-of-use and peak demand charges) and a discomfort penalty, which is an extension of most reward functions used in existing DRL works in this area. Moreover, we develop a reward shaping technique to overcome the issue of reward sparsity caused by the demand charge. Through a single-zone building simulation platform, we demonstrate that the customized DQN outperforms the baseline rule-based policy, saving close to 6% of total cost with demand charges, while close to 8% without demand charges.
Quality control and quality assurance are challenges in direct metal laser melting (DMLM). Intermittent machine diagnostics and downstream part inspections catch problems after undue cost has been ...incurred processing defective parts. In this paper we demonstrate two methodologies for in-process fault detection and part quality prediction that leverage existing commercial DMLM systems with minimal hardware modification. Novel features were derived from the time series of common photodiode sensors along with standard machine control signals. In one methodology, a Bayesian approach attributes measurements to one of multiple process states as a means of classifying process deviations. In a second approach, a least squares regression model predicts severity of certain material defects.
A key reason for using asynchronous computer conferencing in instruction is its potential for supporting collaborative learning. However, few studies have examined collaboration in computer ...conferencing. This study examined collaboration in six peer review groups within an asynchronous computer conferencing. Eighteen tertiary students participated in the study. Content analyses of discussion protocols were performed in terms of participation, interaction, and social presence. The results indicate that collaboration does not occur automatically in asynchronous computer conference. Collaboration requires participation because no collaboration occurred in the two groups with low student participation; however, participation does not lead to collaboration, evidenced by student postings receiving no peer responses. Collaboration requires interaction but does not end with interaction, substantiated by different levels of collaboration across different interactional patterns. Social presence helps to realise collaboration through establishing a warm and collegial learning community to encourage participate and interaction, exemplified by the contrast of the group with the highest level of social presence and the group with the lowest level of social presence. A model of understanding and assessing collaboration in online learning is recommended, consisting of participation, interaction and social presence.
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