Abstract—Remote interrogation of surface acoustic wave ID-
tags imposes a high signal amplitude which is related to a high coupling coefficient value (K 2 ) and low propagation losses (α). In this paper, we propose and discuss an alternative configuration to the standard one. Here, we replaced the conventional configuration, i.e. one interdigital transducer (IDT) and several reflectors, by a series of electrically connected IDTs. The goal is to increase the amplitude of the detected signal using direct transmission between IDTs instead of the reflection from passive reflectors. This concept can therefore increase the interrogation scope of ID-tags made on conventional substrate with high K 2 value. Moreover, it can also be extended to suitable substrates for harshenvironments such as high temperature environments: the materials used exhibit limited performances (low K 2 value and relatively high propagation losses) and are therefore rarely used for identification applications. The concept was first tested and validated using the lithium niobate 128°Y-X cut substrate, which is commonly used in ID-tags. A good agreement between experimental and numerical results was obtained for the promising concept of connected IDTs. The interesting features of the structure were also validated using a langasite substrate, which is well-known to operate at very high temperatures. Performances of both substrates (lithium niobate and langasite) were tested with an in-situ RF characterization up to 600°C. Unexpected results regarding the resilience of devices based on congruent lithium niobate were obtained.
Zayan EL Khaled and Hamid Mcheick
The failure of communications systems may cause catastrophic damage to human life and economic activities as people are unable to communicate with each other in a timely manner and with a convenient quality of service. Therefore, the exchange of information is more than necessary for people in their everyday life or during harshenvironments to pre- vent the death and injury of thousands of individuals. The study of communications systems behavior in harsh environ- ments helps to design or select more resilient technologies that are capable of operating in challenging conditions. This article reviews existing approaches, major causes of failure, and weaknesses of communications systems during extreme events. First, we highlight the importance of communications systems, and then we examine related works, how commu- nication may fail, and the effect of this failure on human life in general and during extreme events response. Furthermore, we study and analyze how communications are used during various stages of extreme events, and we iden- tify the main weaknesses and limitations that communications systems may suffer based on many case studies. To con- clude, we identify and discuss relevant attributes, requirements, and recommendations for communications systems to perform with a suitable quality of service during harshenvironments and to reduce risks of communication failure in challenging conditions.
environments favor species with traits typical of stress resistance syndrome (Chapin et al. 1993; Grime et al. 1997; Aerts and Chapin 2000), we expected that in both stony and sandy grasslands there would be a higher proportion of the strategies near the stress tolerance corner of the triangle (i.e., S, S-SC, S/SR and S/CSR). On the other hand, since stony and sandy grasslands have consistently distinct micro environmental features (e.g., amount of plant cover, proportion of fine soil and degree of soil fertility), we expect that these differences will filter distinct functional strategies and features in each habitat (i.e., there would be a significant connection between habitat structure and functional identity of these two herbaceous communities).
worst gratings, as reported in Table II. Moreover, this error is reduced to less than 1 °C for the grating written in the PSC fiber.
V. C ONCLUSION
In this work we show the preliminary study that has to be performed to determine and identify both the adapted fiber and the Bragg grating photo-inscription conditions to realize a strain and/or temperature sensor suitable for a harsh environment. The F-doped SMF showed the lowest RIA value at 1550 nm among the analyzed samples at an accumulated dose of 1 MGy. The choice of a Ge-free fiber promotes the fs-radiation, as the one we used operating at 800 nm, for the grating inscription. On the con- trary of the RIA, no strong dependence of the fs-FBGs’ radiation sensitivity on the fiber composition was observed. Moreover, the blue-shift of the Bragg peak at 1 MGy dose corresponds to an error on the temperature measurement lower than 2.5 °C.
In this contribution, based on the preliminary results in [ 24 ], where we proposed an augmented state extended Kalman filter (EKF) to cope with possible UWB anchor position mismatch under nominal Gaussian conditions, we further explore robust TOA-based navigation in realistic scenarios with model mismatch and affected by harsh propagation conditions. We consider that several transmitter to receiver links may be affected by multi-path or NLOS conditions, then we assume the typical contamination model arising in robust statistics [ 26 ] for a subset of (corrupted) ranging measurements. Without model mismatch, a possible solution is to consider a robust regression-based EKF [ 26 ], but this methodology does not apply when both outliers and model mismatch are present, mainly because the filter cannot distinguish between true measurement outliers and measurements which deviate from the nominal due to the mismatch. Therefore, we propose new robust filtering strategies able to cope with both effects. Illustrative realistic simulation results are provided to support the discussion and show the performance improvement brought by these new robust TOA-based navigation methodologies.
Several techniques can be used to extend the lifetime of the sensors used in these harshenvironments by reducing the impact of these pixels exhibiting high dark current values. First, the use of very small integration time will significantly reduce the number of integrated dark electron (the total number of dark charges in a frame is simply the product of the dark current and the integration time). Clearly, the 1 s integration time used in this experiment is not a best case from the dark current point of view (a few milliseconds would be enough to integrate the useful signal). Another option that is often used is to cool down the sensor, since the dark current is known to drop exponentially with temperature. Finally, the dark frame subtraction operation mentioned previously, also contributes to reduce the impact of hot pixels on the image quality.
Fig. 7: Insertion loss deviation (∆IL) recorded over oil contamination (MIL-PRF-7808), water contamination and dust particle contamination (talc powder 10 microns) compared with contaminant free connections, for a SMF GIF LC connection, a SMF LC
connection and a MMF LC connection, each time with 10 mating cycles
Such a behavior makes utilization of such connectors in harshenvironments very useful especially in sensor applications. Moreover thanks to the high misalignment tolerances as demonstrated in paragraph 2, these expanded beam connectors are less sensitive to thermal induced mechanical expansion.
Abstract—Research on the shortest path in networks to maintain connectivity in the Internet of Things (IoT) remains an important issue for determining minimal routes, especially in terms of time and distance, between two devices at distinct points (i.e., nodes) of the network. Many constraints exist for IoT smart devices for transmitting a large amount of information and data, such as limited resources, energy, and time consumption, as well as the potential for overwhelmed communication traffic. Several algorithms were designed and implemented to address these problems that can be simulated and considered as information message passing. The search space is often modeled by a graph, where each node corresponds to a location of a smart device, and the edges represent the paths or links that carry messages, while the absence of a path between two nodes designates a communication breakdown or obstacle. Existing pathfinding algorithms are incorporated in applications, such as Google Maps, rescue people, video games, online packet routing, and rescue applications used in harshenvironments. For these latter scenarios, the infrastructure for various technologies of communication becomes vulnerable and dysfunctional, so maintaining connectivity and finding the shortest path becomes a priority. Our goal is to remedy this problem by taking advantage of modernized peer-to-peer wireless technologies, such as Wi-Fi Direct, which can be improved through autonomous wireless technology kits like Lopy 4 of Pycom, and through two alternatives of moving devices (nodes) or service drones. This paper investigates several shortest path algorithms and identifies three case studies to maintain connectivity in harshenvironments.
1 I NTRODUCTION
Navigation is a key task for any virtual reality application. The user should be able to modify their viewpoint in order to explore, search or maneuver in the virtual environment . However, although a wide range of navigation interfaces exist (e.g. locomotion inter- faces, flying interfaces), few works have addressed how the naviga- tion speed can be adjusted in order to ensure a smooth and pleasant navigation experience. In rate-control interfaces, the range of the input device is mapped into a fixed range of acceptable navigation speeds. This range might not be optimal for a wide range of vir- tual environments, resulting on motions that are potentially too fast (Which can induce motion sickness ) or too slow (decreasing user engagement).
V. C ONCLUSION
In this work, we proposed an innovative framework aiming to assess attention in virtual reality environments. It aims to have better knowledge on the mechanisms behind attention and to be able to detect the loss and gain of attention from physiological signals, e.g. Electroencephalogram, eyes information (pupils size, saccade) or head-movement. The detector created could be used in further work to design neurofeedback for children with ADHD in virtual reality. Besides, to provide an emotionally comfortable environment by allowing the participant to make her choice, the framework presents encouraging results regarding the classification of states of attention. Three different machine learning-based classifiers have been tested on feature vectors built from the physiological signals and can predict well the attention state in many cases.
These random models define parametric classes of urban environments morphologicaly equivalent. We present in Appendix B key functions to simulate efficiently a large number of representative environments for each class and set of parameters.
In what follows, we illustrate the interest of these models by studying the environment’s mean morphology impact over the path loss function of an electromagnetic wave emanating from a placed-high antenna to any user at the ground level, at a distance d of the antenna. The commonly admitted rule of thumb is that P (d) ' d −α with α0 depending on the environment.
A social welfare function is a procedure for aggregating proles of individual prefer- ences into social orderings. Arrow's theorem shows that it is impossible for a social welfare function to satisfy weak Pareto (if all individuals strictly prefer one alterna- tive to another, then so does society), independence of irrelevant alternatives (the social ranking of two alternatives only depends on the individual rankings of these al- ternatives), and non-dictatorship when the preference domain is unrestricted. When the set of alternatives is structured, the assumption of unrestricted domain might be unreasonable. One important exception of this kind are spatial environments. In spa- tial environments, alternatives are points in a Euclidean space of issue positions and individual preferences are continuous, quasi-concave, and have bliss points. Although the assumption of unrestricted domain is unreasonable in economic and spatial en- vironments, it has been shown that Arrow's theorem remains valid in most of these environments. 1
In spatial environments, we consider social welfare functions satisfying Arrow's requirements, i.e., weak Pareto and independence of irrelevant alternatives. When the policy space is a one-dimensional continuum, such a welfare function is determined by a collection of 2 N strictly quasi-concave preferences and a tie-breaking rule. As a corollary, we obtain that when the number of voters i i s odd, simple majority voting is transitive if and only if each voter's preference is strictly quasi-concave. When the policy space is multi-dimensional, we establish Arrow's impossibility theorem. Among others, we show that weak Pareto, independence of irrelevant alternatives, and non-
Institute For Information Technology, National Research Council Canada
Creating geometrically correct and complete 3D models of complex environments remains a difficult problem. Techniques for 3D digitizing and modeling have been rapidly advancing over the past few years although most focus on single objects or specific applications such as architecture and city mapping. The ability to capture details and the degree of automation vary widely from one approach to another. One can safely say that there is no single approach that works for all types of environment and at the same time is fully automated and satisfies the requirements of every application. In this paper we show that for complex environments, those composed of several objects with various characteristics, it is essential to combine data from different sensors and information from different sources. Our approach combines models created from multiple images, single images, and range sensors. It can also use known shapes, CAD, existing maps, survey data, and GPS. 3D points in the image-based models are generated by photogrammetric bundle adjustment with or without self-calibration depending on the image and point configuration. Both automatic and interactive procedures are used depending on the availability of reliable automated process. Producing high quality and accurate models, rather than full automation, is the goal. Case studies in diverse environments are used to demonstrate that all the aforementioned features are needed for environments with a significant amount of complexity.