We describe experimental vignette methodology (EVM) as a way to address the dilemma of conducting experimental research that results in high levels of confidence regarding internal validity but is challenged by threats to external validity versus conducting nonexperimental research that usually maximizes external validity but whose conclusions are ambiguous regarding causal relationships. EVM studies consist of presenting participants with carefully constructed and realistic scenarios to assess dependent variables including intentions, attitudes, and behaviors, thereby enhancing experimental realism and also allowing researchers to manipulate and control independent variables. We describe two major types of EVM aimed at assessing explicit (i.e., paper people studies) and implicit (i.e., policy capturing and conjoint analysis) processes and outcomes. We offer best practice recommendations regarding the design and implementation of EVM studies based on a multidisciplinary literature review, discuss substant...

Best Practice Recommendations for Designing and Implementing Experimental Vignette Methodology Studies

With much advancement in the field of nanotechnology, bioengineering, and synthetic biology over the past decade, microscales and nanoscales devices are becoming a reality. Yet the problem of engineering a reliable communication system between tiny devices is still an open problem. At the same time, despite the prevalence of radio communication, there are still areas where traditional electromagnetic waves find it difficult or expensive to reach. Points of interest in industry, cities, and medical applications often lie in embedded and entrenched areas, accessible only by ventricles at scales too small for conventional radio waves and microwaves, or they are located in such a way that directional high frequency systems are ineffective. Inspired by nature, one solution to these problems is molecular communication (MC), where chemical signals are used to transfer information. Although biologists have studied MC for decades, it has only been researched for roughly 10 year from a communication engineering lens. Significant number of papers have been published to date, but owing to the need for interdisciplinary work, much of the results are preliminary. In this survey, the recent advancements in the field of MC engineering are highlighted. First, the biological, chemical, and physical processes used by an MC system are discussed. This includes different components of the MC transmitter and receiver, as well as the propagation and transport mechanisms. Then, a comprehensive survey of some of the recent works on MC through a communication engineering lens is provided. The survey ends with a technology readiness analysis of MC and future research directions.

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A Comprehensive Survey of Recent Advancements in Molecular Communication

Chemotactic bacteria are guided towards the source of a nutrient by local concentration gradients. That works on the microscopic scale, but at larger scales such local cues are unreliable pointers — for example, wind or water currents may disperse odours sought by foraging animals. Using statistical techniques, Vergassola et al. have developed a general search algorithm for movement strategies based on the detection of sporadic cues and partial information. The strategy, termed 'infotaxis' as it maximizes the expected rate of information gain, could find application in the design of 'sniffer' robots. A computational model of odour plume propagation and experimental data are used to devise a general search algorithm for movement strategies in chemotaxis, based on sporadic cues and partial information. The strategy is termed 'infotaxis' as it locally maximizes the expected rate of information gain. Chemotactic bacteria rely on local concentration gradients to guide them towards the source of a nutrient1. Such local cues pointing towards the location of the source are not always available at macroscopic scales because mixing in a flowing medium breaks up regions of high concentration into random and disconnected patches. Thus, animals sensing odours in air or water detect them only intermittently as patches sweep by on the wind or currents2,3,4,5,6. A macroscopic searcher must devise a strategy of movement based on sporadic cues and partial information. Here we propose a search algorithm, which we call ‘infotaxis’, designed to work under such conditions. Any search process can be thought of as acquisition of information on source location; for infotaxis, information plays a role similar to concentration in chemotaxis. The infotaxis strategy locally maximizes the expected rate of information gain. We demonstrate its efficiency using a computational model of odour plume propagation and experimental data on mixing flows7. Infotactic trajectories feature ‘zigzagging’ and ‘casting’ paths similar to those observed in the flight of moths8. The proposed search algorithm is relevant to the design of olfactory robots9,10,11, but the general idea of infotaxis can be applied more broadly in the context of searching with sparse information.

"Infotaxis" as a strategy for searching without gradients

A comprehensive review is presented on the development and state of the art of colorimetric and fluorometric sensor arrays. Optical arrays based on chemoresponsive colorants (dyes and nanoporous pigments) probe the chemical reactivity of analytes, rather than their physical properties. This provides a high dimensionality to chemical sensing that permits high sensitivity (often down to ppb levels), impressive discrimination among very similar analytes and exquisite fingerprinting of extremely similar mixtures over a wide range of analyte types, both in the gas and liquid phases.

https://zenodo.org/record/895426/files/article.pdf

Optical sensor arrays for chemical sensing: the optoelectronic nose

A comprehensive review on the development and state of the art of colorimetric and fluorometric sensor arrays is presented Chemical sensing aims to detect subtle changes in the chemical environment by transforming relevant chemical or physical properties of molecular or ionic species (ie, analytes) into an analytically useful output Optical arrays based on chemoresponsive colorants (dyes and nanoporous pigments) probe the chemical reactivity of analytes, rather than their physical properties (eg, mass) The chemical specificity of the olfactory system does not come from specific receptors for specific analytes (eg, the traditional lock-and-key model of substrate-enzyme interactions), but rather olfaction makes use of pattern recognition of the combined response of several hundred olfactory receptors In a similar fashion, arrays of chemoresponsive colorants provide high-dimensional data from the color or fluorescence changes of the dyes in these arrays as they are exposed to analytes This provides chemical sensing with high sensitivity (often down to parts per billion levels), impressive discrimination among very similar analytes, and exquisite fingerprinting of extremely similar mixtures over a wide range of analyte types, in both the gas and liquid phases Design of both sensor arrays and instrumentation for their analysis are discussed In addition, the various chemometric and statistical analyses of high-dimensional data (including hierarchical cluster analysis (HCA), principal component analysis (PCA), linear discriminant analysis (LDA), support vector machines (SVMs), and artificial neural networks (ANNs)) are presented and critiqued in reference to their use in chemical sensing A variety of applications are also discussed, including personal dosimetry of toxic industrial chemical, detection of explosives or accelerants, quality control of foods and beverages, biosensing intracellularly, identification of bacteria and fungi, and detection of cancer and disease biomarkers

The Optoelectronic Nose: Colorimetric and Fluorometric Sensor Arrays.

A new device has been developed for generating airflow field and odor-concentration distribution in a real environment for presenting to the user. This device is called a multi-sensorial field (MSF) display. When two fans are placed facing each other, the airflows generated by them collide with each other and are radially deflected on a plane perpendicular to the original airflow direction. By utilizing the deflected airflow, the MSF display can present the airflow blowing from the front to the user without placing fans in front of the user. The directivity of the airflow deflection can be controlled by placing nozzles on the fans to adjust the cross-sectional shape of the airflow jets coming from the fans. The MSF display can also generate odor-concentration distribution in a real environment by introducing odor vapors into the airflow generated by the fans. The user can freely move his/her head and sniff at various locations in the generated odor distribution. The results of preliminary sensory tests are presented to show the potential of the MSF display.

Multi-sensorial field display: Presenting spatial distribution of airflow and odor

A new sensing system for gas-source localization is proposed. Gas molecules released from their source are carried by airflow and form an aerial trail called a plume. The authors' group has been developing smart sensing systems and robots that can track gas flows and find their sources for, e.g., fire alarming and detection of flammable or hazardous gas leakage. The present report demonstrates the first sensing system that has accomplished sensitive detection and reliable tracking of gas plumes in real-life indoor environments. An ultrasonic anemometer is used to accurately measure the 3D vector of the airflow direction. Six tin-oxide semiconductor gas sensors are placed around the anemometer to estimate the 3D direction of the gas concentration gradient. The direction to follow is obtained by combining those two vectors. The experimental results show that the proposed system can track a gas plume formed in a field of airflow as low as 3 cm/s.

http://ieeexplore.ieee.org/iel5/9624/30805/01426387.pdf

Three-dimensional gas-plume tracking using gas sensors and ultrasonic anemometer

A new method to find a gas/odor source is proposed. A portable homogeneous gas sensor array is used to visualize the flow of a target gas. The direction of a gas source is estimated using a real-time image processing algorithm, and the source is located by following the estimated direction. The design of the sensor array has been performed using the simulation technique developed in the previous study. In the designing process, a virtual sensor array with an arbitrary time constant is placed in a dynamic gas distribution field visualized using a tracer such as smoke of joss sticks. The virtual sensor array behavior, which is much slower than the gas concentration change, is then calculated by inputting the optical data, captured by a video camera, to the sensor dynamics model. As a result, the designed system has been found effective through the simulation.

Study of real-time visualization of gas/odor flow image using gas sensor array

This paper addresses the problem of estimating proximity to a gas source using concentration measurements. In particular, we consider the problem of gas source declaration by a mobile robot equipped with metal oxide sensors in a turbulent indoor environment. While previous work has shown that machine learning classifiers can be trained to detect close proximity to a gas source, it is difficult to interpret the learned models. This paper investigates possible underlying indicators of gas source proximity, comparing three different statistics derived from the sensor measurements of the robot. A correlation analysis of 1056 trials showed that response variance (measured as standard deviation) was a better indicator than average response. An improved result was obtained when the standard deviation was normalized to the average response for each trial, a strategy that also reduces calibration problems

Indicators of Gas Source Proximity using Metal Oxide Sensors in a Turbulent Environment

A new method to remotely locate an odor source using a mobile robot with a gas sensor is proposed. Although several odor-source localization systems have been already reported, the source location is not known until those systems finally arrive at the location. Since the proposed method enables the estimation of the distance to the source simultaneously with its direction, the source can be remotely located. Furthermore, the release rate of the odor and the range of its distribution can be obtained using this method. This feature is realized by moving the robot and fitting the gas distribution model to the gas sensor response at each location considering the response delay. The soundness of the method is shown by the experiments on ethanol-gas-source localization in a clean room.

Hiroshi Ishida

Papers

Multi-sensorial field display: Presenting spatial distribution of airflow and odor

Three-dimensional gas-plume tracking using gas sensors and ultrasonic anemometer

Study of real-time visualization of gas/odor flow image using gas sensor array

Indicators of Gas Source Proximity using Metal Oxide Sensors in a Turbulent Environment

Remote sensing and localization of gas/odor source and distribution using mobile sensing system