fixed typo #9

paper/paper.md

@@ -28,7 +28,7 @@ This paper presents a digital twin prototype of the [PiCar-X by Sunfounder](http
 # Statement of need
 Digital twins are becoming increasingly relevant in the the Industrial Internet of Things and Industry 4.0 [@kritzinger:2018], as they enhance existing capabilities for monitoring and controlling cyber-physical systems. This is achieved by integrating a digital representation of the real system in the form of a digital model. However, the concept of digital twins lacks a consensual definition and faces validation challenges, partly due to the scarcity of reproducible modules or source codes in existing studies. While many applications are described in case studies, they often lack detailed, re-usable specifications for researchers and engineers. This can lead to confusions, since modern simulations or enhanced climate models are also often praised as digital twins [@barbie:2024].
 
-In [@barbie:2024], we formally specified a digital twin concept including its sub-concepts physical twin, digital model, digital template, digital thread, digital shadow, digital twin, and digital twin prototype using the Object-Z notation and they a the basis for this paper and the PiCar-X example. These concepts were developed for a network of ocean observation systems and the results were evaluated in a real-world mission in the Baltic sea in Oktober 2020 [@demomission:2020]. One of the results of the successful proof-of-concept was the ARCHES Digital Twin Framework [@ADTF:2022], a software package providing the functionality to implement the digital thread between physical twins and digital twins for data and command exchange.
+In [@barbie:2024], we formally specified a digital twin concept including its sub-concepts physical twin, digital model, digital template, digital thread, digital shadow, digital twin, and digital twin prototype using the Object-Z notation and they are the basis for this paper and the PiCar-X example. These concepts were developed for a network of ocean observation systems and the results were evaluated in a real-world mission in the Baltic sea in Oktober 2020 [@demomission:2020]. One of the results of the successful proof-of-concept was the ARCHES Digital Twin Framework [@ADTF:2022], a software package providing the functionality to implement the digital thread between physical twins and digital twins for data and command exchange.
 Ocean observation systems use quite specific and expensive hardware, hence, we see the need of a cheap lab experiemnt to enable independent evaluation and exploration of the different concepts. The PiCar-X example demonstrates all the concepts from the ocean observation system and includes also a full integration test pipeline, see our GitHub Repository [@archespicarx:2024]. In [@barbiepicarx:2024], we elaborate in more detail how the PiCar-X can be used to evaluate all these concepts and how they differ from each other in possible code implementations.
 
 
@@ -43,15 +43,15 @@ Lacking official CAD files for the PiCar-X, we utilized a simplified CAD model o
 
 ![The CAD model used for the PiCar-X digital model in a GAZEBO simulation.\label{fig:picarx-dm}](./img/picarx-dm.jpg){ width=70% }
 
-We provide Docker compose files that can be used to run the software with either the digital model, digital shadow, digital twin, or digital twin prototype.
+We provide Docker compose files that can be used to run the software with either the digital shadow, digital twin, or digital twin prototype.
 
 # The Digital Twin Prototype for Development and Automated Integration Testing in CI/CD Pipelines
 Developing a physical twin typically requires connecting the hardware to a development environment. However, in such a setup, only one person can use the hardware at a time. For a team of engineers, this means either everyone needs their own PiCar-X or they must take turns, which can become costly, especially in real-world applications like full-scale vehicles.
 A digital twin prototype can reduce the need for additional hardware for each team member by serving as the software counterpart of a physical twin, with identical configurations [@barbie:2024]. However, instead of physical sensors and actuators, emulators are used to mimic their functions. 
 
 The core of the digital twin prototype approach involves replacing all physical sensors and actuators with emulations or simulations, effectively virtualizing the hardware interfaces. As a result, the device driver cannot - and does not need to - distinguish between a real sensor/actuator and its emulated equivalent. The ARCHES PiCar-X uses emulators connected to a [GAZEBO](https://gazebosim.org/) simulation. The simulation provides the virtual context for the emulators, instead of using recordings from previous runs.
 
-For the PiCar, the primary interfaces, GPIO and I2C, are emulated using Linux kernel tools. The virtual GPIO interaction module (gpio-mockup) and the I2C chip (I2C-stub) are integrated into the container for these emulation purposes. This example also works on computers running on Windows with the Linux subsystem (WSL2). This setup provides a flexible and adaptable environment for emulating the PiCar's hardware interactions. The configuration of the digital twin prototype is illustrated in \autoref{fig:picarx-dtp}. The digital twin prototype can also be started using the provided Docker compose files.
+For the PiCar-X, the primary interfaces, GPIO and I2C, are emulated using Linux kernel tools. The virtual GPIO interaction module (gpio-mockup) and the I2C chip (I2C-stub) are integrated into the container for these emulation purposes. This example also works on computers running on Windows with the Linux subsystem (WSL2). This setup provides a flexible and adaptable environment for emulating the PiCar's hardware interactions. The configuration of the digital twin prototype is illustrated in \autoref{fig:picarx-dtp}. The digital twin prototype can also be started using the provided Docker compose files.
 
 ![The digital twin prototype of the PiCar-X.\label{fig:picarx-dtp}](./img/picarx-dtp.jpg)