NO Detection by Pulsed Polarization of Lambda Probes-Influence of the Reference Atmosphere

The pulsed polarization measurement technique using conventional thimble type lambda probes is suitable for low ppm NOx detection in exhaust gas applications. To evaluate the underlying sensor mechanism, the unknown influence of the reference atmosphere on the NO sensing behavior is investigated in this study. Besides answering questions with respect to the underlying principle, this investigation can resolve the main question of whether a simplified sensor element without reference may be also suitable for NO sensing using the pulsed polarization measurement technique. With an adequate sensor setup, the reference atmosphere of the thimble type lambda probe is changed completely after a certain diffusion time. Thus, the sensor response regarding NO is compared with and without different gas atmospheres on both electrodes. It is shown that there is still a very good NO sensitivity even without reference air, although the NO response is reduced due to non-existing overlying mixed potential type voltage, which is otherwise caused by different atmospheres on both electrodes. Considering these results, we see an opportunity to simplify the standard NOx sensor design by omitting the reference electrode

A primer on coupled state-switching models for multiple interacting time series

State-switching models such as hidden Markov models or Markov-switching regression models are routinely applied to analyse sequences of observations that are driven by underlying non-observable states. Coupled state-switching models extend these approaches to address the case of multiple observation sequences whose underlying state variables interact. In this paper, we provide an overview of the modelling techniques related to coupling in state-switching models, thereby forming a rich and flexible statistical framework particularly useful for modelling correlated time series. Simulation experiments demonstrate the relevance of being able to account for an asynchronous evolution as well as interactions between the underlying latent processes. The models are further illustrated using two case studies related to a) interactions between a dolphin mother and her calf as inferred from movement data; and b) electronic health record data collected on 696 patients within an intensive care unit.Comment: 30 pages, 9 figure

Pragmatic order selection in hidden Markov models

Pohle JM, Langrock R. Pragmatic order selection in hidden Markov models. In: Proceedings of the 32nd IWSM Vol. 1. 2017

Detection of NOx in Combustion Engine Exhaust Gas by Applying the Pulsed Polarization Technique on YSZ Based Sensors

The pulsed polarization measurement technique applied on sensor devices based on yttria stabilized zirconia (YSZ) with porous platinum electrodes enables the detection of low ppm concentrations of NOx in exhaust gas applications with a simple device. Pulsed polarization is based on alternating voltage pulses with intermediate pauses for self discharging. The discharge characteristics after polarization depends strongly on NOx content in the low ppm range. Due to faster discharging in NOx containing atmospheres compared to base gas, the voltage difference between the discharge curves can act as a concentration dependent parameter. Sensor probes for usage in exhaust gas conditions have been built. The feasibility of NOx sensing in diesel exhaust gas by use of a planar cost-effective YSZ sensor element is evaluated in detail in comparison to commercial NOx exhaust sensors and referenced with gas analysis equipment

Modeling interactions between individuals using coupled hidden Markov models

Pohle JM, Ötting M, Jensen FH, Langrock R. Modeling interactions between individuals using coupled hidden Markov models. In: Proceedings of the 34th International Workshop on Statistical Modelling. Volume I. 2019: 57-61

Coupled Markov-switching regression: inference and a case study using electronic health record data

Pohle JM, King R, van der Schaar M, Langrock R. Coupled Markov-switching regression: inference and a case study using electronic health record data. In: Proceedings of the 33rd International Workshop on Statistical Modelling, Vol. 1. 2018: 242-246

Selecting the Number of States in Hidden Markov Models: Pragmatic Solutions Illustrated Using Animal Movement

Pohle J, Langrock R, van Beest FM, Schmidt NM. Selecting the Number of States in Hidden Markov Models: Pragmatic Solutions Illustrated Using Animal Movement. Journal of Agricultural, Biological and Environmental Statistics. 2017;22(3):270–293

Scalable fabrication of individual SWNT chem-FETs for gas sensing

We present a scalable, Deep-UV (220 nm) photolithography based process for fabricating low-power gas sensors integrating an individual single-walled carbon nanotube (SWNT) as a sensing element. SWNTs grow from defined catalyst (ferritin) islands, and their density is controlled by controlling the catalyst particle density. By designing the electrode dimensions based on the length distribution of SWNTs, a single-SWNT bridging yield of 30% has been achieved. Furthermore, we show that exposure to NO2 at room temperature results in a positive shift of the threshold voltage. A threshold shift of approximately 2 V for 500 ppb of NO2 is observed. The presented process also enables the possibility of fabricating carbon nanotube sensor arrays, as a large number of single-tube devices can be fabricated in each process run

Analyte Detection with Cu-BTC Metal–Organic Framework Thin Films by Means of Mass-Sensitive and Work-Function-Based Readout

Metal–organic frameworks (MOFs) constitute a new generation of porous crystalline materials, which have recently come into focus as analyte-specific active elements in thin-film sensor devices. Cu-BTCalso known as HKUST-1is one of the most theoretically and experimentally investigated members of the MOF family. Its capability to selectively adsorb different gas molecules renders this material a promising candidate for applications in chemical gas and vapor sensing. Here, we explore details of the host–guest interactions between HKUST-1 and various analytes under different environmental conditions and study the vapor adsorption mechanism by mass-sensitive and work-function-based readouts. These complementary transduction mechanisms were successfully applied for the detection of low ppm (2 to 50 ppm) concentrations of different alcohols (methanol, ethanol, 1-propanol, and 2-propanol) adsorbed into Cu-BTC thin films. Evaluation of the results allows for the comparison of the amounts of adsorbed vapors and the contribution of each vapor to the changes of the electronic properties of Cu-BTC. The influence of the length of the alcohol chain (C1–C3) and geometry (1-propanol, 2-propanol) as well as their polarity on the sensing performance was investigated, revealing that in dry air, short chain alcohols are more likely adsorbed than long chain alcohols, whereas in humid air, this preference is changed, and the sensitivity toward alcohols is generally decreased. The adsorption mechanism is revealed to differ for dry and humid atmospheres, changing from a site-specific binding of alcohols to the open metal sites under dry conditions to weak physisorption of the analytes dissolved in surface-adsorbed water reservoirs in humid air, with the signal strength being governed by their relative concentration