Unexpected Disconnections Research Articles

Dimensioning payload size for fast retransmission of MQTT packets in the wake of network disconnections

The Internet of Things (IoT) is spreading rapidly around the world, and Message Queue Telemetry Transport (MQTT) is one of the main protocols used to explore device-to-device (D2D) communication. The industry typically requires communication systems that can transmit data continuously while optimizing both bandwidth and transmission time. Due to the vast amount of data that can be lost, companies often find that even short periods of network downtime lead to significant costs. In this paper, we propose a retransmission mechanism to allow sensor nodes to relay missing data via MQTT to a local server when it reconnects after an unexpected disconnection. To assess its performance, several tests in a digital healthcare use case scenario have been designed. Since the procedure involves transferring a considerable amount of data, our main goal is to determine the maximum payload of each message to restore the missing information, while minimizing the retransmission time without information loss.

신재생에너지 수용증대를 고려한 주파수조정용 전기저장장치의 1차 예비력 대체효과 정량화 방법

In the Korean power system, the Primary Frequency Response (PFR) is provided by the Battery Energy Storage System (BESS) as well as the generator governor for arresting the frequency excursion caused by an unexpected disconnection of generation units. However, given that the frequency response performance of BESS is superior to that of the existing governor response, it is important to configure the required amount of PFR with generators and BESS for the stable and efficient operation of the power system especially when the penetration level of Renewable Energy Sources (RES) is highly increased. Therefore, in this paper, the PFR contribution effect by BESS was quantified by determining the substitutable governor response quantity considering the penetration of RES, when the BESS provides the PFR using the control algorithm implemented in the operating site. Further, the quantification of the PFR substitution effect by BESS using the proposed method is performed in the Korean power system under renewable penetration scenarios. The results prove the validity of the proposed method and show that the PFR substitution effect by BESS increases as the penetration of RES increases.

Dynamic and adaptive fault-tolerant asynchronous federated learning using volunteer edge devices

The number of devices, from smartphones to IoT hardware, interconnected via the Internet is growing all the time. These devices produce a large amount of data that cannot be analyzed in any data center or stored in the cloud, and it might be private or sensitive, thus precluding existing classic approaches. However, studying these data and gaining insights from them is still of great relevance to science and society. Recently, two related paradigms try to address the above problems. On the one hand, edge computing (EC) suggests to increase processing on edge devices. On the other hand, federated learning (FL) deals with training a shared machine learning (ML) model in a distributed (non-centralized) manner while keeping private data locally on edge devices. The combination of both is known as federated edge learning (FEEL). In this work, we propose an algorithm for FEEL that adapts to asynchronous clients joining and leaving the computation. Our research focuses on adapting the learning when the number of volunteers is low and may even drop to zero. We propose, implement, and evaluate a new software platform for this purpose. We then evaluate its results on problems relevant to FEEL. The proposed decentralized and adaptive system architecture for asynchronous learning allows volunteer users to yield their device resources and local data to train a shared ML model. The platform dynamically self-adapts to variations in the number of collaborating heterogeneous devices due to unexpected disconnections (i.e., volunteers can join and leave at any time). Thus, we conduct comprehensive empirical analysis in a static configuration and highly dynamic and changing scenarios. The public open-source platform enables interoperability between volunteers connected using web browsers and Python processes. We show that our platform adapts well to the changing environment getting a numerical accuracy similar to today’s configurations using a given number of homogeneous (hardware and software) computers as a static platform for learning. We demonstrate the fault-tolerance of the platform in self-recovering from unexpected disconnections of volunteer devices. We then prove that EC, coupled with FL, can lead to scientific tools that can be practical involving real users for final competitive numerical results in real problems for science and society.

Focal Times and Spaces: How Ethnography Foregrounds the Spatiotemporality of International Organizations and Global Governance

AbstractDrawing on a long‐term political ethnography of sites of global health governance, the paper makes methodological and substantive contributions. First of all, it shows that ethnography induces researchers to experience international organizations (IOs) and global governance as spatiotemporal phenomena. This experience overlaps with the lived realities of practitioners and spotlights aspects that are otherwise easily overlooked. Both practitioners and ethnographers have to be in specific spaces at particular times. This practical challenge illustrates that there are focal times and spaces, which are linked to the cyclical and sited character of global health governance. These focal times and spaces provide an important coordination mechanism and ease the general flow of knowledge – within IOs and between IOs and their environment. However, there is also the constant danger that they develop a self‐referential life of their own and become disconnected from other processes. Similarly, not just researchers but also practitioners are struggling to develop a comprehensive understanding of IOs since they experience them only partially and in specific settings. Thus, a spatiotemporal account highlights both overlooked links and unexpected disconnections. The conclusion mentions that the current – COVID‐19‐induced – mainstreaming of digital technologies will impact the spatiotemporal dimension of global health governance.

Inadvertent Detachment of Stent Retrievers during Mechanical Thrombectomy—A Clinical and Biomechanical Perspective

Background: The inadvertent detachment of stent retrievers during mechanical thrombectomy is an extremely rare but feared complication associated with poor clinical outcomes. We discuss management considerations after an unexpected disconnection of the pRESET stent retriever during mechanical thrombectomy, based on clinical experience and mechanical and phantom studies. Methods: We present a clinical course of rare accidents of stent-retriever separation inside an intracranial vessel that occurred in patients in a comprehensive stroke centre between 2018 and 2020. We designed a phantom study to assess the Tigertriever’s ability to remove a detached stent retriever from intercranial vessels. In the mechanical study, several types of stent retrievers were evaluated in order to find the weakest point at which detachment occurred. Results: Two patients (~0.7%) with inadvertent stent-retriever detachment were found in our database. Failed attempts of endovascular removal with no recanalization at the end of procedure were reported in both cases. mRS after 3 months was three and four respectively. In the mechanical study, the Tigertriever was the most resistant to detachment and was followed by Embotrap > pRESET > 3D Separator. In the phantom study, the pRESET device detached in a configuration resembling the M1 segment was successfully removed with the Tigertriever. Conclusions: Conservative management of the inadvertent detachment of stent retrievers during mechanical thrombectomy in large vessel occlusion may be acceptable in order to avoid further periprocedural complications after unsuccessful device removal attempts. Based on the phantom and mechanical studies, the Tigertriever may be a useful tool for the removal of detached pRESET devices.

Si-Backside Protection Circuits Against Physical Security Attacks on Flip-Chip Devices

This article presents a cryptographic key protection technique from physical security attacks through Si-backside of IC chip. Flip-chip packaging leads to a serious security hole that allows emerging backside physical security attacks. The proposed backside buried metal (BBM) structure forming a meander wire pattern on the Si-backside detects unexpected disconnection of the meander and warns the malicious attempts to expose a vulnerable Si substrate. Moreover, the BBM meander also shields key information of cryptographic circuit from both passive side-channel attacks and active laser fault injection as well. Unlike other conventional laminate-based protection, this backside monolithic approach does not require frontside wiring resources or additional packaging layers, resulting in only 0.0025% size-overhead. The BBM meander was formed on the backside of a 0.13- $\mu \text{m}$ CMOS cryptographic chip by wafer-level via-last BBM processing.

Electric Vehicle Charging Management Using Auction Mechanism for Reducing PV Curtailment in Distribution Systems

This paper proposes an electric vehicle (EV) charging management scheme for effective utilization of photovoltaic (PV) power based on an auction mechanism. The proposed scheme coordinates an amount of self-consumption of PV output by shifting the charging period of customers' EVs, and it reduces PV curtailment caused by voltage rise in low-voltage distribution systems (LVDSs). The auction mechanism is introduced in order to assure both the equity of benefit in each customer and the autonomy that enables customers to voluntarily participate in the EV charging management scheme. The authors perform numerical simulations based on a Japanese distribution system model and evaluate the effectiveness of the proposed scheme. The results show that our proposed scheme reduces the residential operation cost and the PV curtailment in LVDSs without an enhanced communication network even taking into consideration the effects of forecasting errors of electricity demand and PV output, and unexpected disconnection condition of several EVs.

Network-Coded Cooperation and Multi-Connectivity for Massive Content Delivery

Massive content delivery is in the spotlight of the research community as both data traffic and the number of connected mobile devices are increasing at an incredibly fast pace. The enhanced mobile broadband (eMBB) is one of the main use cases for the fifth generation of mobile networks (5G), which focuses on transmitting greater amounts of data at higher data rates than in the previous generations, but also on increasing the area capacity (given in bits per second per square meter) and reliability. However, the broadcast and multicast implementation in 5G and presents several drawbacks such as unexpected disconnections and the lack of device-specific QoS guarantees. As a result, whenever the exact same content is to be delivered to numerous mobile devices simultaneously, this content must be replicated. Hence, the same number of parallel unicast sessions as users are needed. Therefore, novel systems that provide efficient massive content delivery and reduced energy consumption are needed. In this paper, we present a network-coded cooperation (NCC) protocol for efficient massive content delivery and the analytical model that describes its behavior. The NCC protocol combines the benefits of cooperative architectures known as mobile clouds (MCs) with Random Linear Network Coding (RLNC). Our results show the benefits of our NCC protocol when compared to the establishment of numerous parallel unicast sessions are threefold: offload data traffic from the cellular link, reduce the energy consumption at the cooperating users, and provide throughput gains when the cellular bandwidth is insufficient.

Algoritmo adaptativo para protecciones de sobrecorriente en el caso de estudio IEEE9

Una adecuada coordinación de protecciones eléctricas es fundamental en los sistemas de potencia, con el fin de evitar desconexiones inesperadas que pueden desencadenar problemas en la operación de la red eléctrica y sus diferentes componentes. Aunque esta actividad tiene una alta complejidad en sistemas de gran tamaño, actualmente existen algunos métodos de coordinación de protecciones automáticos, los cuales han sido aplicados en casos de estudio. En este documento se desarrolla un algoritmo adaptativo de coordinación de cuatro relés de sobrecorriente direccionales, que se encuentran en dos líneas de transmisión adyacentes en el caso de estudio de nueve barras IEEE 9; dos protecciones por cada línea de transmisión seleccionada. Posteriormente se encuentra un análisis de los resultados obtenidos, explicando ciertas características del sistema de potencia y relacionándolas con el comportamiento de los parámetros de los relés ante los cambios en la topología de este. Finalmente, se mencionan las conclusiones sobre dichos resultados y el desempeño del algoritmo. Los aportes de este trabajo radican en el análisis de una alternativa innovadora en Colombia, que permita optimizar el uso del esquema de protecciones en un sistema de potencia. Asimismo, los resultados obtenidos permiten validar la implementación del algoritmo en equipos reales, para un piloto sobre un segmento de la red, el cual es propiedad de CODENSA.

Let nature decide its nature: On the design of collaborative hyperheuristics for decentralized ephemeral environments

The research community has traditionally aimed at the derivation and development of metaheuristic solvers, suited to deal with problems of very diverse characteristics. Unfortunately, it is often the case that new metaheuristic techniques are presented and assessed in a reduced set of cases, mostly due to the lack of computational resources to undertake extensive performance studies over a sufficiently diverse set of optimization benchmarks. This manuscript explores how ephemeral environments could be exploited to efficiently construct metaheuristic algorithms by virtue of a collaborative, distributed nature-inspired hyperheuristic framework specifically designed to be deployed over unreliable, uncoordinated computation nodes. To this end, the designed framework defines two types of nodes (trackers and peers, similarly to peer-to-peer networks), both reacting resiliently to unexpected disconnections of nodes disregarding their type. Peer nodes exchange their populations (i.e. constructed algorithms) asynchronously, so that local optima are avoided at every peer thanks to the contribution by other nodes. Furthermore, the overall platform is fully scalable, allowing its users to implement and share newly derived operators and fitness functions so as to enrich the diversity and universality of the heuristic algorithms found by the framework. Results obtained from in-lab experiments with a reduced number of nodes are discussed to shed light on the evolution of the best solution of the framework with the number of connected peers and the tolerance of the network to node disconnections.

Self assembly of anastomosis-like superstructures in fatty acid/guanidine hydrochloride aqueous dispersions

A mixture between 1% sodium myristate and guanidine hydrochloride at a molar ratio of 1 in water forms a gel of membranes below a phase transition of ca. 21 °C and a viscous limpid and isotropic solution above. As observed by both TEM and AFM, we report the formation of interconnected superstructures in that latter phase. Those assemblies exhibit a size of ca. 4–40 nm width and several tens of μm length with unexpected disconnections and re-connections between them having the appearance of an anastomosis-like superstructure.