Towards a process model for service systems

Service Science is a new interdisciplinary approach to the study, design, implementation. and innovation of service systems. However due to the variety in service research, there is no consensus yet about the theoretical foundation of this domain. As a basis for a common understanding of service systems and their interactions, Service Science researchers Spohrer and Kwan proposed the service systems worldview. The ISPAR model was presented as a part of this service systems worldview as a tool for identifying ten possible interaction episodes, i.e., the sequences of activities that are undertaken by two interacting service system entities. In this paper we evaluate the use of the ISPAR model as a process model for service systems. We identify the shortcomings of the ISPAR model and propose possible improvements. This analysis leads to the development of a new service process model which is demonstrated through tree different examples

Substrate integrated waveguide textile antennas as energy harvesting platforms

Textile multi-antenna systems are key components of smart fabric and interactive textile (SFIT) systems, as they establish reliable and energy-efficient wireless body-centric communication links. In this work, we investigate how their functionality can further be extended by exploiting their surface as an energy harvesting and power management platform. We provide guidelines for selecting an appropriate antenna topology and describe a suitable integration procedure. We demonstrate this approach by integrating two flexible solar cells, a micro-energy cell and a flexible power management system onto a well-chosen wearable substrate integrated waveguide cavity-backed textile slot antenna, without affecting its performance, to enable energy harvesting from solar and artificial light. In addition, the compact and highly-integrated harvesting module provides a terminal for connecting a thermoelectric generator, enabling thermal body energy harvesting. Measurements in a realistic indoor environment have demonstrated that this hybrid energy harvesting approach leverages a more continuous flow of scavenged energy, enabling energy scavenging in most of the indoor and outdoor scenarios

Make the most of your samples : Bayes factor estimators for high-dimensional models of sequence evolution

Background: Accurate model comparison requires extensive computation times, especially for parameter-rich models of sequence evolution. In the Bayesian framework, model selection is typically performed through the evaluation of a Bayes factor, the ratio of two marginal likelihoods (one for each model). Recently introduced techniques to estimate (log) marginal likelihoods, such as path sampling and stepping-stone sampling, offer increased accuracy over the traditional harmonic mean estimator at an increased computational cost. Most often, each model's marginal likelihood will be estimated individually, which leads the resulting Bayes factor to suffer from errors associated with each of these independent estimation processes. Results: We here assess the original 'model-switch' path sampling approach for direct Bayes factor estimation in phylogenetics, as well as an extension that uses more samples, to construct a direct path between two competing models, thereby eliminating the need to calculate each model's marginal likelihood independently. Further, we provide a competing Bayes factor estimator using an adaptation of the recently introduced stepping-stone sampling algorithm and set out to determine appropriate settings for accurately calculating such Bayes factors, with context-dependent evolutionary models as an example. While we show that modest efforts are required to roughly identify the increase in model fit, only drastically increased computation times ensure the accuracy needed to detect more subtle details of the evolutionary process. Conclusions: We show that our adaptation of stepping-stone sampling for direct Bayes factor calculation outperforms the original path sampling approach as well as an extension that exploits more samples. Our proposed approach for Bayes factor estimation also has preferable statistical properties over the use of individual marginal likelihood estimates for both models under comparison. Assuming a sigmoid function to determine the path between two competing models, we provide evidence that a single well-chosen sigmoid shape value requires less computational efforts in order to approximate the true value of the (log) Bayes factor compared to the original approach. We show that the (log) Bayes factors calculated using path sampling and stepping-stone sampling differ drastically from those estimated using either of the harmonic mean estimators, supporting earlier claims that the latter systematically overestimate the performance of high-dimensional models, which we show can lead to erroneous conclusions. Based on our results, we argue that highly accurate estimation of differences in model fit for high-dimensional models requires much more computational effort than suggested in recent studies on marginal likelihood estimation

Dual-band substrate integrated waveguide textile antenna with integrated solar harvester

A dual-band wearable textile antenna based on substrate integrated waveguide technology is presented for operation in the [2.4-2.4835]-GHz Industrial, Scientific and Medical band and the [2.5-2.69]-GHz 4G LTE band 7. The antenna features an integrated flexible solar harvesting system, consisting of a flexible solar cell, a power management system, and energy storage. All these components are judiciously positioned on the antenna platform in order not to affect its radiation performance. The measured reflection coefficients and radiation characteristics after bending and deploying the antenna on a human body prove that the antenna is well suited for on-body use. A measured on-body antenna gain and radiation efficiency of 5.0 dBi and 89% are realized. Measurements in a real-life situation have demonstrated the ability to scavenge a maximum of 53 mW by means of a single integrated flexible solar cell

Dual-polarized 28-GHz air-filled SIW phased antenna array for next-generation cellular systems

A high-performance dual-polarized eight-element air-filled substrate-integrated-waveguide (AFSIW) cavity-backed patch antenna array is presented. The antenna operates in the [26.5-29.5] GHz band and provides a stable high data-rate wireless communication link between end-user terminals and access points in next-generation cellular systems. Its topology is carefully selected to maximize the performance of the array. In addition, by combining the AFSIW technology with a new antenna architecture, a low-profile, low-cost, stable, and high-performance array design is guaranteed. A prototype was fabricated and validated, demonstrating a wide active impedance bandwidth over ±35 o scanning range and low-cross polarization level within the entire frequency band

Wearable, small, and robust: the circular quarter-mode textile antenna

A miniaturized wearable antenna, entirely implemented in textile materials, is proposed that relies on a quarter-mode substrate integrated waveguide topology. The design combines compact dimensions with high body-antenna isolation, making it excellently suited for off-body communication in wearable electronics/smart textile applications. The fabricated antenna achieves stable on-body performance. A measured on-body impedance matching bandwidth of 5.1% is obtained, versus 4.8% in free space. The antenna gain equals 3.8 dBi in the on-body and 4.2 dBi for the free-space scenario. High radiation efficiency, measured to be 81% in free space, is combined with a low calculated specific absorption rate of 0.45 mW/g, averaged over 1 g of tissue, with 500 mW input power

The next generation textile antennas based on substrate integrated waveguide technology

Textile antennas for body-worn applications have some very specific requirements and needs. From an electrical engineer's point of view, good radiation characteristics and impedance matching to the active electronics are important. From the wearer's perspective, the antenna should be unobtrusively integrated into the clothing, and the smart textile comfortable to wear. New techniques offer the potential to fulfill these different needs. One new approach consists of applying metalized eyelets to implement substrate integrated waveguide technology on textile materials. This results in high-performance on-body antennas with excellent behavior in close proximity of the human body. Two realizations are discussed: a wideband design and a miniaturized half mode substrate integrated waveguide dual-band design. Both yield excellent free-space and on-body performance, and superb antenna-body isolation, automatically resulting in very robust characteristics when deployed on-body

Highly efficient impulse-radio ultra-wideband cavity-backed slot antenna in stacked air-filled substrate integrated waveguide technology

An impulse-radio ultra-wideband (IR-UWB) cavity-backed slot antenna covering the [5.9803; 6.9989] GHz frequency band of the IEEE 802.15.4a-2011 standard is designed and implemented in an air-filled substrate integrated waveguide (AFSIW) technology for localization applications with an accuracy of at least 3 cm. By relying on both frequency and time-domain optimization, the antenna achieves excellent IR-UWB characteristics. In free-space conditions, an impedance bandwidth of 1.92 GHz (or 29.4%), a total efficiency higher than 89%, a front-to-back ratio of at least 12.1 dB, and a gain higher than 6.3 dBi are measured in the frequency domain. Furthermore, a system fidelity factor larger than 98% and a relative group delay smaller than 100 ps are measured in the time domain within the 3 dB beamwidth of the antenna. As a result, the measured time-of-arrival of a transmitted Gaussian pulse, for different angles of arrival, exhibits variations smaller than 100 ps, corresponding to a maximum distance estimation error of 3 cm. Additionally, the antenna is validated in a real-life worst-case deployment scenario, showing that its characteristics remain stable in a large variety of deployment scenarios. Finally, the difference in frequency-and time-domain performance is studied between the antenna implemented in AFSIW and in dielectric filled substrate integrated waveguide (DFSIW) technology. We conclude that DFSIW technology is less suitable for the envisaged precision IR-UWB localization application

Four-element ultrawideband textile cross array for dual-spatial and dual-polarization diversity

The emergence of miniaturized flexible electronics enables on-duty first responders to collect biometrical and environmental data through multiple on-body sensors, integrated into their clothing. However, gathering these life-saving data would be useless if they cannot set up reliable, preferable high-data-rate, wireless communication links between the sensors and a remote base station. Therefore, we have developed a four-element ultrawideband textile cross array that combines dual-spatial and dual-polarization diversity and is easily deployable in a first responder's garment. The impedance bandwidth of the array equals 1.43 GHz, while mutual coupling between its elements remains below -25 dB. For a maximal bit error rate of 1e-4, the array realizes a diversity gain of 24.81 dB. When applying adaptive subcarrier modulation, the mean throughput per orthogonal frequency division multiplexing (OFDM) subcarrier increases by an extra bit/symbol when comparing fourth- to second-order diversity