scholarly journals Search on a Line by Byzantine Robots

2021 ◽  
pp. 1-19
Author(s):  
Jurek Czyzowicz ◽  
Konstantinos Georgiou ◽  
Evangelos Kranakis ◽  
Danny Krizanc ◽  
Lata Narayanan ◽  
...  
Keyword(s):  
Lower Bounds ◽  
Fault Tolerant ◽  
Sufficient Evidence ◽  
Maximum Speed ◽  
Parallel Search ◽  
Not Given ◽  
Running Time ◽  
Byzantine Faults ◽  
Infinite Line ◽  
Design Algorithms

We consider the problem of fault-tolerant parallel search on an infinite line by [Formula: see text] robots. Starting from the origin, the robots are required to find a target at an unknown location. The robots can move with maximum speed [Formula: see text] and can communicate wirelessly among themselves. However, among the [Formula: see text] robots, there are [Formula: see text] robots that exhibit byzantine faults. A faulty robot can fail to report the target even after reaching it, or it can make malicious claims about having found the target when in fact it has not. Given the presence of such faulty robots, the search for the target can only be concluded when the non-faulty robots have sufficient evidence that the target has been found. We aim to design algorithms that minimize the value of [Formula: see text], the time to find a target at a (unknown) distance [Formula: see text] from the origin by [Formula: see text] robots among which [Formula: see text] are faulty. We give several different algorithms whose running time depends on the ratio [Formula: see text], the density of faulty robots, and also prove lower bounds. Our algorithms are optimal for some densities of faulty robots.

scholarly journals Fundamental limitations on distillation of quantum channel resources

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Bartosz Regula ◽  
Ryuji Takagi
Keyword(s):  
Lower Bounds ◽  
Quantum Channel ◽  
Quantum Communication ◽  
Fault Tolerant ◽  
State Of The Art ◽  
Quantum Systems ◽  
Noisy Channels ◽  
General Transformation ◽  
Fundamental Limitations ◽  
Strong Converse

AbstractQuantum channels underlie the dynamics of quantum systems, but in many practical settings it is the channels themselves that require processing. We establish universal limitations on the processing of both quantum states and channels, expressed in the form of no-go theorems and quantitative bounds for the manipulation of general quantum channel resources under the most general transformation protocols. Focusing on the class of distillation tasks — which can be understood either as the purification of noisy channels into unitary ones, or the extraction of state-based resources from channels — we develop fundamental restrictions on the error incurred in such transformations, and comprehensive lower bounds for the overhead of any distillation protocol. In the asymptotic setting, our results yield broadly applicable bounds for rates of distillation. We demonstrate our results through applications to fault-tolerant quantum computation, where we obtain state-of-the-art lower bounds for the overhead cost of magic state distillation, as well as to quantum communication, where we recover a number of strong converse bounds for quantum channel capacity.

Byzantine Fault-Tolerant Architecture in Cloud Data Management

2019 ◽  
pp. 889-902
Author(s):  
Mohammed A. AlZain ◽  
Alice S. Li ◽  
Ben Soh ◽  
Mehedi Masud
Keyword(s):  
Cloud Computing ◽  
Data Management ◽  
Service Provider ◽  
Fault Tolerant ◽  
Academic Research ◽  
Point Of View ◽  
Cloud Data ◽  
Byzantine Faults ◽  
Byzantine Fault ◽  
Cloud Data Management

One of the main challenges in cloud computing is to build a healthy and efficient storage for securely managing and preserving data. This means a cloud service provider needs to make sure that its clients' outsourced data are stored securely and, data queries and retrievals are executed correctly and privately. On the other hand, it may also mean businesses are willing to outsource their data to a third party only if they trust their data are not accessible and visible to the service provider and other non-authorized parties. However, one of the major obstacles faced here for ensuring data reliability and security is Byzantine faults. While Byzantine fault tolerance (BFT) has received growing attention from the academic research community, the research done is generally from the distributed computing point of view, and hence finds little practical use in cloud computing. To that end, the focus of this paper is to discuss how these faults can be tolerated with the authors' proposed conceptualization of Byzantine data faults and fault-tolerant architecture in cloud data management.

Byzantine Fault-Tolerant Architecture in Cloud Data Management

2016 ◽  
Vol 7 (3) ◽  
pp. 86-98 ◽  
Author(s):  
Mohammed A. AlZain ◽  
Alice S. Li ◽  
Ben Soh ◽  
Mehedi Masud
Keyword(s):  
Cloud Computing ◽  
Data Management ◽  
Service Provider ◽  
Fault Tolerant ◽  
Academic Research ◽  
Third Party ◽  
Cloud Data ◽  
Byzantine Faults ◽  
Byzantine Fault ◽  
Cloud Data Management

One of the main challenges in cloud computing is to build a healthy and efficient storage for securely managing and preserving data. This means a cloud service provider needs to make sure that its clients' outsourced data are stored securely and, data queries and retrievals are executed correctly and privately. On the other hand, it may also mean businesses are willing to outsource their data to a third party only if they trust their data are not accessible and visible to the service provider and other non-authorized parties. However, one of the major obstacles faced here for ensuring data reliability and security is Byzantine faults. While Byzantine fault tolerance (BFT) has received growing attention from the academic research community, the research done is generally from the distributed computing point of view, and hence finds little practical use in cloud computing. To that end, the focus of this paper is to discuss how these faults can be tolerated with the authors' proposed conceptualization of Byzantine data faults and fault-tolerant architecture in cloud data management.

scholarly journals The image of absence and the politics of naming in Shona war fiction

Literator ◽  
2013 ◽  
Vol 34 (1) ◽  
Author(s):  
Willie L. Chigidi ◽  
Davie E. Mutasa
Keyword(s):  
Young People ◽  
Political Rhetoric ◽  
Sufficient Evidence ◽  
Not Given ◽  
Female Characters ◽  
War Fiction ◽  
War Novels ◽  
Guerrilla War ◽  
Masculine Discourse

During Zimbabwe’s liberation war thousands of young people crossed into neighbouring countries to take up arms to fight and end colonialism. There is sufficient evidence that many of these young people were women. Political rhetoric also maintains that women fought alongside their male counterparts. However, in the Shona literature that depicts Zimbabwe’s guerrilla war there is a glaring absence of female characters who play the roles of guerrilla fighters. This article is an attempt to discuss this absence and to explain why there are very few guerrilla girls in Shona war fiction. The article argues that female guerrillas are not given much space in Shona war novels because the writers of these novels continue the oral folktale tradition in which women are rarely made heroines. It is further argued that in the actual guerrilla war of the 1970s female guerrillas were rarely seen fighting at the war front, that the pioneer guerrillas were men and that the masculine discourse about the war excluded women. Moreover, only men have written Shona war novels.

scholarly journals Clique Is Hard on Average for Regular Resolution

2021 ◽  
Vol 68 (4) ◽  
pp. 1-26
Author(s):  
Albert Atserias ◽  
Ilario Bonacina ◽  
Susanna F. De Rezende ◽  
Massimo Lauria ◽  
Jakob Nordström ◽  
...  
Keyword(s):  
Lower Bound ◽  
Lower Bounds ◽  
State Of The Art ◽  
Edge Density ◽  
Multiplicative Constant ◽  
Running Time ◽  
Maximum Cliques

We prove that for k ≪ 4√ n regular resolution requires length n Ω( k ) to establish that an Erdős–Rényi graph with appropriately chosen edge density does not contain a k -clique. This lower bound is optimal up to the multiplicative constant in the exponent and also implies unconditional n Ω( k ) lower bounds on running time for several state-of-the-art algorithms for finding maximum cliques in graphs.

scholarly journals On The Independence Number Of Some Strong Products Of Cycle-Powers

2015 ◽  
Vol 40 (2) ◽  
pp. 133-141 ◽  
Author(s):  
Marcin Jurkiewicz ◽  
Marek Kubale ◽  
Krzysztof Ocetkiewicz
Keyword(s):  
Lower Bounds ◽  
Independence Number ◽  
Computational Results ◽  
Shannon Capacity ◽  
Noisy Channels ◽  
Running Time ◽  
The Third ◽  
Independence Numbers

Abstract In the paper we give some theoretical and computational results on the third strong power of cycle-powers, for example, we have found the independence numbers α((C102)√3) = 30 and α((C144)√3) = 14. A number of optimizations have been introduced to improve the running time of our exhaustive algorithm used to establish the independence number of the third strong power of cycle-powers. Moreover, our results establish new exact values and/or lower bounds on the Shannon capacity of noisy channels.

Clock synchronization in distributed multicomputer systems. Part II

2021 ◽  
Author(s):  
I.V. Asharina
Keyword(s):  
Technology Development ◽  
Fault Tolerant ◽  
Clock Synchronization ◽  
Fault Model ◽  
Complex Task ◽  
Space Applications ◽  
Synchronization Process ◽  
Byzantine Faults ◽  
Characteristic Features ◽  
Modern Technologies

The study substantiates the necessity of clock synchronization in distributed multicomputer systems. The basic definitions related to the concept of clock synchronization are given, and methods of clock synchronization are classified. Increasing the lifecycle of failure- and fault-tolerant distributed multicomputer systems for critical application is one of the most urgent problems at the current level of technology development. This is especially true for unattended distributed multicomputer systems for space applications. The second part deals with synchronization in systems with Byzantine faults, and this is a complex task due to the characteristic features of the fault model. The synchronization process in multi-cluster and multi-complex systems is associated with the multitasking of such systems, which makes the synchronization process even more relevant and multi-criteria. The paper considers the modern technologies providing the synchronization process in systems of critical use.

Exponential Lower Bounds for the Running Time of DPLL Algorithms on Satisfiable Formulas

2006 ◽  
Vol 35 (1-3) ◽  
pp. 51-72 ◽  
Author(s):  
Michael Alekhnovich ◽  
Edward A. Hirsch ◽  
Dmitry Itsykson
Keyword(s):  
Lower Bounds ◽  
Running Time
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