Filters








64 Hits in 1.5 sec

Reliable Restricted Process Theory [article]

Fatemeh Ghassemi, Wan Fokkink
2017 arXiv   pre-print
Malfunctions of a mobile ad hoc network (MANET) protocol caused by a conceptual mistake in the protocol design, rather than unreliable communication, can often be detected only by considering communication among the nodes in the network to be reliable. In Restricted Broadcast Process Theory, which was developed for the specification and verification of MANET protocols, the communication operator is lossy. Replacing unreliable with reliable communication invalidates existing results for this
more » ... esults for this process theory. We examine the effects of this adaptation on the semantics of the framework with regard to the non-blocking property of communication in MANETs, the notion of behavioral equivalence relation and its axiomatization. We illustrate the applicability of our framework through a simple routing protocol. To prove its correctness, we introduce a novel proof process, based on a precongruence relation.
arXiv:1705.02600v1 fatcat:rnje4f33xbclfaawy7feleqpma

Verification of Asynchronous Systems with an Unspecified Component [article]

Rosa Abbasi, Fatemeh Ghassemi, Ramtin Khosravi
2017 arXiv   pre-print
Component-based systems evolve as a new component is added or an existing one is replaced by a newer version. Hence, it is appealing to assure the new system still preserves its safety properties. However, instead of inspecting the new system as a whole, which may result in a large state space, it is beneficial to reuse the verification results by inspecting the newly added component in isolation. To this aim, we study the problem of model checking component-based asynchronously communicating
more » ... sly communicating systems in the presence of an unspecified component against safety properties. Our solution is based on assume-guarantee reasoning, adopted for asynchronous environments, which generates the weakest assumption. If the newly added component conforms to the assumption, then the whole system still satisfies the property. To make the approach efficient and convergent, we produce an overapproximated interface of the missing component and by its composition with the rest of the system components, we achieve an overapproximated specification of the system, from which we remove those traces of the system that violate the property and generate an assumption for the missing component. We have implemented our approach on two case studies. Furthermore, we compared our results with the state of the art direct approach. Our resulting assumptions are smaller in size and achieved faster.
arXiv:1709.03245v1 fatcat:qpgx54hezfcsvgx6qopmsxq7w4

Hybrid Rebeca: Modeling and Analyzing of Cyber-Physical Systems [article]

Iman Jahandideh, Fatemeh Ghassemi, Marjan Sirjani
2019 arXiv   pre-print
In cyber-physical systems like automotive systems, there are components like sensors, actuators, and controllers that communicate asynchronously with each other. The computational model of actor supports modeling distributed asynchronously communicating systems. We propose Hybrid Rebeca language to support modeling of cyber-physical systems. Hybrid Rebeca is an extension of actor-based language Rebeca. In this extension, physical actors are introduced as new computational entities to
more » ... ities to encapsulate physical behaviors. To support various means of communication among the entities, the network is explicitly modeled as a separate entity from actors. We derive hybrid automata as the basis for analysis of Hybrid Rebeca models. We demonstrate the applicability of our approach through a case study in the domain of automotive systems. We use SpaceEx framework for the analysis of the case study.
arXiv:1901.02597v1 fatcat:4me7pspqyfajda77ovxeoy4rpy

An Efficient Loop-free Version of AODVv2 [article]

Behnaz Yousefi, Fatemeh Ghassemi
2017 arXiv   pre-print
Ad hoc On Demand distance Vector (AODV) routing protocol is one of the most prominent routing protocol used in Mobile Ad-hoc Networks (MANETs). Due to the mobility of nodes, there exists many revisions as scenarios leading to the loop formation were found. We demonstrate the loop freedom property violation of AODVv2-11, AODVv2-13, and AODVv2-16 through counterexamples. We present our proposed version of AODVv2 precisely which not only ensures loop freedom but also improves the performance.
arXiv:1709.01786v2 fatcat:vhxsegtvyjdrrpgltyvlho5yiq

Artifacts in Macular Optical Coherence Tomography

Fatemeh Bazvand, Fariba Ghassemi
2020 Journal of Current Ophthalmology  
To identify and explain different artifacts in macular optical coherence tomography (OCT). For this comprehensive review, a PubMed and Google Scholar (January 1995-October 2018) search was conducted by the researchers, using the keywords such as OCT, artifacts, artefact, and macula. We reviewed the main OCT artifacts including software break-down or misidentification of retinal layers, incomplete segmentation error, complete segmentation failure, mirror artifact (inverted artifact), cut edge
more » ... ifact), cut edge artifact, degraded image scan, out-of-register artifact, off-center artifact, motion artifact, foveal duplication, segmentation shift, blink artifact, static or fixed image artifact, linear artifact, and perfluorocarbon liquid-producing artifact. There are various artifacts in OCT image scans. The identification of these artifacts may help in accurate interpretations of OCT images in clinical settings that can affect the diagnosis and management of different retinal disorders.
doi:10.4103/joco.joco_83_20 pmid:32671295 pmcid:PMC7337029 fatcat:xw7nrvomofgbrdgjflq54j4dvq

Equational Reasoning on Ad Hoc Networks [chapter]

Fatemeh Ghassemi, Wan Fokkink, Ali Movaghar
2010 Lecture Notes in Computer Science  
We provide an equational theory for Restricted Broadcast Process Theory to reason about ad hoc networks. We exploit an extended algebra called Computed Network Theory to axiomatize restricted broadcast. It allows one to define an ad hoc network with respect to the underlying topologies. We give a sound and complete axiomatization for the recursion-free part of the term algebra CNT, modulo what we call rooted branching computed network bisimilarity.
doi:10.1007/978-3-642-11623-0_6 fatcat:wgnohv3rfvfdfbik2hm7jie7xu

Stochastic Restricted Broadcast Process Theory [chapter]

Fatemeh Ghassemi, Mahmoud Talebi, Ali Movaghar, Wan Fokkink
2011 Lecture Notes in Computer Science  
We provide a framework for modeling and analyzing both qualitative and quantitative aspects of mobile ad hoc network (MANET) protocols above the data-link layer. We extend Restricted Broadcast Process Theory [11, 9] : delay functions are assigned to actions, while the semantics captures the interplay of a MANET protocol with stochastic behavior of the data-link and physical layer, and the dynamic topology. A continuous-time Markov chain is derived from our semantic model by resolving
more » ... esolving non-determinism, using the notion of weak Markovian network bisimilarity. The framework is applied to a leader election algorithm.
doi:10.1007/978-3-642-24749-1_7 fatcat:wknfanphajc5nkghspd2haq7z4

Model Checking MANETs with Arbitrary Mobility [chapter]

Fatemeh Ghassemi, Saeide Ahmadi, Wan Fokkink, Ali Movaghar
2013 Lecture Notes in Computer Science  
Modeling arbitrary connectivity changes of mobile ad hoc networks (MANETs) makes application of automated formal verification challenging. We introduced constrained labeled transition systems (CLTSs) as a semantic model to represent mobility. To model check MANET protocol with respect to the underlying topology and connectivity changes, we here introduce a branching-time temporal logic interpreted over CLTSs. The temporal operators, from Action Computation Tree Logic with an unless operator,
more » ... unless operator, are parameterized by multi-hop constraints over topologies, to express conditions on successful scenarios of a MANET protocol. We moreover provide a bisimilarity relation with the same distinguishing power for CLTSs as our logical framework.
doi:10.1007/978-3-642-40213-5_14 fatcat:dxzpljcsiff5pmdtcm44ognrcm

Formal Modeling and Analysis of Medical Systems [chapter]

Mahsa Zarneshan, Fatemeh Ghassemi, Marjan Sirjani
2020 Lecture Notes in Computer Science  
Medical systems are composed of medical devices and apps which are developed independently by different vendors. A set of communication patterns, based on asynchronous message-passing, has been proposed to loosely integrate medical devices and apps. These patterns guarantee the point-to-point quality of communication service (QoS) by local inspection of messages at its constituent components. These local mechanisms inspect the property of messages to enforce a set of parametrized local QoS
more » ... ized local QoS properties. Adjusting these parameters to achieve the required point-to-point QoS is non-trivial and depends on the involved components and the underlying network. We use Timed Rebeca, an actor-based formal modeling language, to model such systems and asses their QoS properties by model checking. We model the components of communication patterns as distinct actors. A composite medical system using several instances of patterns is subject to state-space explosion. We propose a reduction technique preserving QoS properties. We prove that our technique is sound and show the applicability of our approach in reducing the state space by modeling a clinical scenario made of several instances of patterns. schema to describe the communication needs of devices/apps. These communication patterns, based on asynchronous message-passing, facilitate development and forensic analysis of clinical scenarios. The use of message passing as the basic communication model is quite common in Internet of Things applications. While the individual components can be very different and operate independently, their interactions typically expose and deliver important emergent properties [2] . These communication patterns consist of a set of components which are responsible to check a set of quality of service (QoS) properties locally. The combination of these quality of service properties should guarantee point-topoint communication requirements. These local QoS properties are parametrized by a set of thresholds on timing behavior of messages like the interval time between consequent messages, the lifetime of messages, etc. A medical system may use several instances of such patterns among its constituent devices and apps. Adjusting these parameters is non-trivial and depends not only to the architecture of the system but also the underlying network. Communication failures in medical systems may result in loss of life. For example, the X-ray machine should stop after two seconds, otherwise it causes harmful prolonged exposure. We can exploit formal methods to verify that the configuration of parameters results the point-to-point communication requirements of medical systems at design time. We use the actor-based formal modeling language of Rebeca [11, 15] to verify medical systems. Actor model is a computational model for event-based distributed systems in which actors communicate by asynchronous messagepassing. The computation model of Rebeca helps to model the communication patterns with minimal effort and mistake. We exploit the timed extension of Rebeca to address local QoS properties defined in terms of the timing behavior of messages. Timed Rebeca [10,13] is supported by the Afra tool which efficiently verifies timed properties by model checking. Timed Rebeca supports inheritance among actors which facilitates modeling of communication patterns that their components communicate with the shared network entity. In this paper we model and analyze communication patterns in Timed Rebeca using the implementation architecture proposed for the communication patterns [9]. The components of patterns are modeled by distinct actors. Since the timing behavior network have effect on satisfying QoS properties of pattern, we also model network as a separate entity from actors. As the number of devices increases in a medical systems, the resulting semantic model may explode which prohibits application of the model checking technique. To tackle the problem, we propose a partial reduction technique for merging states such that the QoS properties of communication patterns are preserved. We prove the correctness of our reduction. We have implemented the reduction technique in a tool in Java which automatically reduces the semantic model generated by Afra. We illustrate the applicability of our reduction technique through a case study on a clinical scenario made of several instances of patterns. Our experimental result shows that our reduction technique can minimize the number of states almost to 30%.
doi:10.1007/978-3-030-50029-0_24 fatcat:6igttd2v6nggdfirxcfvg4kjfi

Neural network-PID controller for roll fin stabilizer

Hassan Ghassemi, Fatemeh Dadmarzi, Parviz Ghadimi, Babak Ommani
2010 Polish Maritime Research  
Fin stabilizers are very effective devices for controlling the ship roll motion against external wave-generated moments. Lift forces due to flow around fin with an angle of attack produce anti -roll moment. Therefore control of attack angle plays important role in reducing roll of ships. This paper presents results of using a combined neural network and PID for roll control of ship with small draught. Numerical results are given of around-fin flow analysis with considering free surface effect
more » ... ee surface effect modelled by neural network and imposed to controlling loop. Hydraulic machinery constraints are also considered in the modelling. The obtained results show good performance of the controller in reducing roll amplitude in random seas. The approach can be used for any irregular sea conditions.
doi:10.2478/v10012-010-0014-3 fatcat:xafdqruqoraadehujaqfdwzjza

Modeling and Efficient Verification of Broadcasting Actors [chapter]

Behnaz Yousefi, Fatemeh Ghassemi, Ramtin Khosravi
2015 Lecture Notes in Computer Science  
Many distributed systems use broadcast communication for various reasons such as saving energy or increasing throughput. However, the actor model for concurrent and distributed systems does not directly support this kind of communication. In such cases, a broadcast must be modeled as multiple unicasts which leads to loss of modularity and state space explosion for any non-trivial system. In this paper, we extend Rebeca, an actor-based model language, to support asynchronous anonymous message
more » ... nonymous message broadcasting. Then, we apply counter abstraction for reducing the state space which efficiently bypasses the constructive orbit problem by considering the global state as a vector of counters, one per each local state. This makes the model checking of systems possible without further considerations of symmetry. This approach is efficient for fully symmetric system like broadcasting environments. We use a couple of case studies to illustrate the applicability of our method and the way their state spaces are reduced in size.
doi:10.1007/978-3-319-24644-4_5 fatcat:jrhgl7v5kzfw7mubrnvnk6qz7q

Product line process theory

Fatemeh Ghassemi, Mohammad Reza Mousavi
2016 Journal of Logical and Algebraic Methods in Programming  
Software product lines (SPLs) facilitate reuse and customization in software development by genuinely addressing the concept of variability. Product Line Calculus of Communicating Systems (PL-CCS) is a process calculus for behavioral modeling of SPLs, in which variability can be explicitly modeled by a binary variant operator. In this paper, we study different notions of behavioral equivalence for PL-CCS, based on Park and Milner's strong bisimilarity. These notions enable reasoning about the
more » ... asoning about the behavior of SPLs at different levels of abstraction. We study the compositionality property of these notions and the mutual relationship among them. We further show how the strengths of these notions can be consolidated in an equational reasoning method. Finally, we designate the notions of behavioral equivalence that are characterized by the property specification language for PL-CCS, called multi-valued modal µ-calculus.
doi:10.1016/j.jlamp.2015.09.008 fatcat:73hvonnnsne2xnzfjufmqqc5xm

Serum hypercoagulability states in Coats' disease

Fariba Ghassemi, Carol L Shields, Masoumeh Mohebbi, Mehdi Nili Ahmadabadi, Fatemeh Morsali, Siamak Sabour
2017 Clinical Ophthalmology  
' disease versus normal controls. your manuscript | www.dovepress.com submit Dovepress Dovepress 306 ghassemi et al Table 2 ) 2 .  ... 
doi:10.2147/opth.s121375 pmid:28223774 pmcid:PMC5308596 fatcat:nqtvsyhulfdy7aupqlokntvjva

Modeling and Efficient Verification of Wireless Ad hoc Networks [article]

Behnaz Yousefi, Fatemeh Ghassemi, Ramtin Khosravi
2017 arXiv   pre-print
Wireless ad hoc networks, in particular mobile ad hoc networks (MANETs), are growing very fast as they make communication easier and more available. However, their protocols tend to be difficult to design due to topology dependent behavior of wireless communication, and their distributed and adaptive operations to topology dynamism. Therefore, it is desirable to have them modeled and verified using formal methods. In this paper, we present an actor-based modeling language with the aim to model
more » ... h the aim to model MANETs. We address main challenges of modeling wireless ad hoc networks such as local broadcast, underlying topology, and its changes, and discuss how they can be efficiently modeled at the semantic level to make their verification amenable. The new framework abstracts the data link layer services by providing asynchronous (local) broadcast and unicast communication, while message delivery is in order and is guaranteed for connected receivers. We illustrate the applicability of our framework through two routing protocols, namely flooding and AODVv2-11, and show how efficiently their state spaces can be reduced by the proposed techniques. Furthermore, we demonstrate a loop formation scenario in AODV, found by our analysis tool.
arXiv:1604.07179v2 fatcat:rbr6kvuuqrhazk6mh7lt75hvuq

Pseudomelanoma at a referral center in iran

Fariba Ghassemi, Fatemeh Bazvand, Seyedeh Simindokht Hosseini
2014 Journal of Ophthalmic & Vision Research  
To report the diagnoses of lesions initially misdiagnosed as ocular melanoma. This retrospective study included all new patients who were referred with a presumptive diagnosis of choroidal melanoma to the ocular oncology clinic at Farabi Eye Hospital from January 2009 to December 2012. Each patient underwent a full ocular examination and B-scan ultrasonography by an ocular oncologist. The final diagnosis was made based on a combination of clinical features, fluorescein angiography, indocyanine
more » ... raphy, indocyanine green angiography, optical coherence tomography, neuroimaging and biopsy when necessary. Out of a total of 194 patients referred with a preliminary diagnosis of choroidal melanoma, 73 (37.6%) subjects actually had pseudomelanoma. Mean age in this subgroup was 46.5±23.1 (range, 1.5-85) years. The most common entities simulating a choroidal melanoma were vasoproliferative tumors (12 cases), choroidal metastasis (11 cases), peripheral exudative hemorrhagic chorioretinopathy (10 cases), lymphoproliferative infiltrative lesions (6 cases) and melanocytoma (5 cases). A wide range of lesions may mimic ocular melanoma; a correct diagnosis may be made by a combination of clinical examination and imaging modalities.
pmid:24982732 pmcid:PMC4074474 fatcat:k3z2zvaxcjfl3chx3asns7dini
« Previous Showing results 1 — 15 out of 64 results