Optimal Byzantine Resilient Convergence in Asynchronous Robot Networks

We propose the first deterministic algorithm that tolerates up to $f$ byzantine faults in $3f+1$-sized networks and performs in the asynchronous CORDA model. Our solution matches the previously established lower bound for the semi-synchronous ATOM model on the number of tolerated Byzantine robots. Our algorithm works under bounded scheduling assumptions for oblivious robots moving in a uni-dimensional space

Mortality from gastrointestinal congenital anomalies at 264 hospitals in 74 low-income, middle-income, and high-income countries: a multicentre, international, prospective cohort study

Background: Congenital anomalies are the fifth leading cause of mortality in children younger than 5 years globally. Many gastrointestinal congenital anomalies are fatal without timely access to neonatal surgical care, but few studies have been done on these conditions in low-income and middle-income countries (LMICs). We compared outcomes of the seven most common gastrointestinal congenital anomalies in low-income, middle-income, and high-income countries globally, and identified factors associated with mortality. // Methods: We did a multicentre, international prospective cohort study of patients younger than 16 years, presenting to hospital for the first time with oesophageal atresia, congenital diaphragmatic hernia, intestinal atresia, gastroschisis, exomphalos, anorectal malformation, and Hirschsprung's disease. Recruitment was of consecutive patients for a minimum of 1 month between October, 2018, and April, 2019. We collected data on patient demographics, clinical status, interventions, and outcomes using the REDCap platform. Patients were followed up for 30 days after primary intervention, or 30 days after admission if they did not receive an intervention. The primary outcome was all-cause, in-hospital mortality for all conditions combined and each condition individually, stratified by country income status. We did a complete case analysis. // Findings: We included 3849 patients with 3975 study conditions (560 with oesophageal atresia, 448 with congenital diaphragmatic hernia, 681 with intestinal atresia, 453 with gastroschisis, 325 with exomphalos, 991 with anorectal malformation, and 517 with Hirschsprung's disease) from 264 hospitals (89 in high-income countries, 166 in middle-income countries, and nine in low-income countries) in 74 countries. Of the 3849 patients, 2231 (58·0%) were male. Median gestational age at birth was 38 weeks (IQR 36–39) and median bodyweight at presentation was 2·8 kg (2·3–3·3). Mortality among all patients was 37 (39·8%) of 93 in low-income countries, 583 (20·4%) of 2860 in middle-income countries, and 50 (5·6%) of 896 in high-income countries (p<0·0001 between all country income groups). Gastroschisis had the greatest difference in mortality between country income strata (nine [90·0%] of ten in low-income countries, 97 [31·9%] of 304 in middle-income countries, and two [1·4%] of 139 in high-income countries; p≤0·0001 between all country income groups). Factors significantly associated with higher mortality for all patients combined included country income status (low-income vs high-income countries, risk ratio 2·78 [95% CI 1·88–4·11], p<0·0001; middle-income vs high-income countries, 2·11 [1·59–2·79], p<0·0001), sepsis at presentation (1·20 [1·04–1·40], p=0·016), higher American Society of Anesthesiologists (ASA) score at primary intervention (ASA 4–5 vs ASA 1–2, 1·82 [1·40–2·35], p<0·0001; ASA 3 vs ASA 1–2, 1·58, [1·30–1·92], p<0·0001]), surgical safety checklist not used (1·39 [1·02–1·90], p=0·035), and ventilation or parenteral nutrition unavailable when needed (ventilation 1·96, [1·41–2·71], p=0·0001; parenteral nutrition 1·35, [1·05–1·74], p=0·018). Administration of parenteral nutrition (0·61, [0·47–0·79], p=0·0002) and use of a peripherally inserted central catheter (0·65 [0·50–0·86], p=0·0024) or percutaneous central line (0·69 [0·48–1·00], p=0·049) were associated with lower mortality. // Interpretation: Unacceptable differences in mortality exist for gastrointestinal congenital anomalies between low-income, middle-income, and high-income countries. Improving access to quality neonatal surgical care in LMICs will be vital to achieve Sustainable Development Goal 3.2 of ending preventable deaths in neonates and children younger than 5 years by 2030

A brief comparative study on analytical models of computer system dependability and security

As two different research topics with much overlap, dependability and security of computer/communication systems have respective long and rich history. The development of the techniques for their modeling and analysis thus have followed distinct but convergent paths. In essence, diverse attributes and the fundamental difference between the nature of the failures bring in different concerns for dependability and security analysis during their modeling process. Taking the understanding of the basic concepts/attributes as a point of departure, this paper intend to carry out a comparative study on the analytical models of computer system dependability and security. Also, by examining the state-of-the-art quantitative techniques and sound modeling methodologies for dependability evaluation, e.g., combinatorial and stochastic methods, we attempt to explore why and how those methods can be extended to evaluate computer system security. Furthermore, we take our developed autonomic detection coordinator (for intrusion detection) as a case study to conduct the comparative analysis.Zonghua Zhang, Hong Shen, Xavier Defago and Yingpeng San

Central banking in transition economies

We study the convergence problem in fully asynchronous, uni-dimensional robot networks that are prone to Byzantine (i.e. malicious) failures. In these settings, oblivious anonymous robots with arbitrary initial positions are required to eventually converge to an a apriori unknown position despite a subset of them exhibiting Byzantine behavior. Our contribution is twofold. We propose a deterministic algorithm that solves the problem in the most generic settings: fully asynchronous robots that operate in the non-atomic CORDA model. Our algorithm provides convergence in 5f + 1-sized networks where f is the upper bound on the number of Byzantine robots. Additionally, we prove that 5f +1 is a lower bound whenever robot scheduling is fully asynchronous. This constrasts with previous results in partially synchronous robots networks, where 3f + 1 robots are necessary and sufficient

Local Algorithms for Autonomous Robot Systems

Abstract. This paper studies local algorithms for autonomous robot systems, namely, algorithms that use only information of the positions of a bounded number of their nearest neighbors. The paper focuses on the spreading problem. It defines measures for the quality of spreading, presents a local algorithm for the one-dimensional spreading problem, prove its convergence to the equally spaced configuration and discusses its convergence rate in the synchronous and semi-synchronous settings. It then presents a local algorithm achieving the exact equally spaced configuration in finite time in the synchronous setting, and proves it is time optimal for local algorithms. Finally, the paper also proposes an algorithm for the two-dimensional case and presents simulation results of its effectiveness

Convergence of Autonomous Mobile Robots with Inaccurate Sensors and Movements

A number of recent studies concern algorithms for distributed control and coordination in systems of autonomous mobile robots. The common theoretical model adopted in these studies assumes that the positional input of the robots is obtained by perfectly accurate visual sensors, that robot movements are accurate, and that internal calculations performed by the robots on (real) coordinates are perfectly accurate as well. The current paper concentrates on the effect of weakening this rather strong set of assumptions, and replacing it with the more realistic assumption that the robot sensors, movement and internal calculations may have slight inaccuracies. Specifically, the paper concentrates on the ability of robot systems with inaccurate sensors, movements and calculations to carry out the task of convergence. The paper presents several impossibility theorems, limiting the inaccuracy allowing convergence, and prohibiting a general algorithm for gathering, namely, meeting at a point, in a finite number of steps. The main positive result is an algorithm for convergence under bounded measurement, movement and calculation errors

Nakdu'l-Kelam İsimli Eseri Işığında Giritli Sırrı Paşanın Peygamberlik Anlayışı

This paper presents liveness properties that need to be preserved by Event-B models of distributed systems. Event-B is a formal technique for development of models of distributed systems related via refinement. In this paper we outline how enabledness preservation and non-divergence are related to the liveness properties of the B models of the distributed systems. We address the liveness issues related to our model of distributed transactions and outline the construction of proof obligations that need to be discharged to ensure liveness

SCORe: a Scalable One-Copy Serializable Partial Replication Protocol

Abstract. In this article we present SCORe, a scalable one-copy serializable partial replication protocol. Differently from any other literature proposal, SCORe jointly guarantees the following properties: (i) it is genuine, thus ensuring that only the replicas that maintain data accessed by a transaction are involved in its processing, and (ii) it guarantees that read operations always access consistent snapshots, thanks to a one-copy serializable multiversion scheme, which never aborts read-only transactions and spares them from any (distributed) validation phase. This makes SCORe particularly efficient in presence of read-intensive workloads, as typical of a wide range of real-world applications. We have integrated SCORe into a popular open source distributed data grid and performed a large scale experimental study with well-known benchmarks using both private and public cloud infrastructures. The experimental results demonstrate that SCORe provides stronger consistency guarantees (namely One-Copy Serializability) than existing multiversion partial replication protocols at no additional overhead

Unconscious eventual consistency with gossips

Abstract. This paper presents a replication protocol that ensures eventual consistency in large-scale distributed systems subject to network partitions and asynchrony. A simulation study shows that the resulting protocol is scalable and achieves high throughput under load. Our protocol does not rely on any form of consensus, which would lead to block the replicas in case of partitions and asynchrony. Our protocol instead ensures that (1) updates are continuously applied to the replicas and (2) no two updates are ever performed in a different order. Gaps might occur during periods of unreliable communication. They are filled whenever connectivity is provided, and consistency is then eventually ensured, but without any conscious commitment. That is, there is no point in the computation when replicas know that consistency is achieved. This unconsciousness is the key to tolerating perpetual asynchrony with no consensus support.